When Connective Tissue Becomes Neurological: A Perspective on Structural Vulnerability, Dynamic Pathology, and the Nervous System

Abstract

Connective tissue supports the mechanical and physiological environment of the nervous system, but an underlying connective-tissue disorder does not by itself establish the cause of neurological symptoms. We examine the neurological relevance of meningeal, ligamentous, spinal, and neurovascular structures in Ehlers–Danlos syndromes (EDSs), distinguishing established disease mechanisms from observational associations and controversial hypotheses. We propose a clinical reasoning framework that begins with a defined neurological phenotype, identifies a plausible physiological mechanism, and then seeks concordant anatomical or physiological evidence. Two illustrative scenarios demonstrate how the approach may justify targeted investigation or, conversely, redirect attention toward more likely nonstructural diagnoses. We distinguish primary Chiari I malformation from acquired tonsillar descent associated with cerebrospinal fluid (CSF) loss; separate evidence-based investigation of spontaneous intracranial hypotension from incompletely validated provocative imaging for suspected craniocervical instability; and critically appraise the limitations of surgical series and occult tethered cord studies. The framework is a proposed aid to reasoning, not a validated diagnostic instrument, and its diagnostic accuracy, safety, resource implications, and effect on patient outcomes remain unknown. Connective-tissue vulnerability should inform hypotheses, not substitute for proof of neurological consequence.

1. Introduction: When Connective Tissue Becomes Neurological

Connective tissue is often considered primarily through its structural manifestations: joint hypermobility, skin extensibility, tissue fragility, skeletal deformity, and vascular complications. Yet connective tissue is not confined to the musculoskeletal system. It contributes to the architecture of nearly every organ and provides structural support, mechanical stability, compartmental integrity, and extracellular signaling throughout the body. The nervous system is no exception. Its function depends upon connective-tissue-rich structures including the meninges, spinal ligaments, intervertebral discs, vascular walls, extracellular matrix, and supporting tissues surrounding peripheral nerves. Disorders affecting connective-tissue integrity therefore have the potential to become neurological disorders when structural vulnerability alters the physical or physiological environment in which neural tissue must function.

The Ehlers–Danlos syndromes (EDSs) provide a particularly informative model through which to consider this relationship. EDS comprises a heterogeneous group of heritable connective-tissue disorders with variable effects on collagen and extracellular-matrix biology. Hypermobile Ehler–Danlos syndrome (hEDS) remains distinct from most other EDS subtypes in that its molecular basis has not been definitively established [1,2]. Neurological and spinal manifestations reported across EDS include Chiari I malformation, craniocervical and segmental instability, spinal deformity, spontaneous cerebrospinal fluid (CSF) leaks, Tarlov cysts, and tethered cord syndrome, although the strength of evidence supporting individual associations varies considerably [3,4,5].

The relationship between connective-tissue vulnerability and neurological disease is consequently neither simple nor deterministic. Hypermobility is not synonymous with instability, structural abnormality is not synonymous with neurological dysfunction, and the presence of a connective-tissue disorder does not establish the cause of a neurological symptom. These distinctions are particularly important in areas such as the craniocervical junction, where physiological mobility is substantial and criteria distinguishing hypermobility from clinically meaningful instability remain incompletely standardized [6,7].

At the same time, an exclusively static view of neurological structure may be insufficient for disorders in which symptoms arise through movement, loading, traction, altered CSF dynamics, or changes in tissue position. The clinical challenge is therefore to determine when anatomical susceptibility produces a physiological consequence capable of altering neural function.

In this perspective, we examine connective-tissue disorders through this neurological framework. This mechanism-centered approach is complementary to recent phenotype-based proposals such as Neuro-EDS, which seek to characterize a neuro-predominant subgroup within hEDS/HSD and related heritable connective-tissue disorders [8]. Our aim here is deliberately narrower: not to define a unified phenotype, but to examine the transition from connective-tissue susceptibility to a specific neurological consequence. Rather than proposing a common structural explanation for heterogeneous neurological symptoms, we consider mechanisms through which connective-tissue vulnerability may become neurologically consequential—including instability, compression, traction, altered CSF dynamics, and meningeal dysfunction—and the evidence linking these mechanisms to specific clinical disorders. Ultimately, the relevant question is not simply whether an anatomical abnormality exists, but when connective-tissue vulnerability becomes neurological disease.

1.1. Literature Selection and Evidentiary Approach

This Perspective draws on the 2017 international EDS classification, neurological and spinal reviews, diagnostic consensus statements, systematic reviews, anatomical investigations, selected observational and surgical series, and relevant controlled studies published through October 2026. Publications were selected for their direct relevance to the proposed anatomical and physiological mechanisms, clinical diagnostic decisions, or conflicting interpretations. Greater interpretive weight was assigned to consensus-based diagnostic standards, systematic reviews, controlled comparisons, and studies with objective outcomes than to uncontrolled surgical cohorts, referral-center case series, and mechanistic hypotheses. This is a narrative Perspective, not a systematic review; searches and selection were not exhaustive, and no formal risk-of-bias scoring or meta-analysis was undertaken. Evidence descriptors in Table 1 indicate the nature and limitations of available evidence rather than validated GRADE ratings.

Table 1. Evidence map for selected neurological and spinal manifestations.

Condition or Proposed Association	Current Evidentiary Interpretation	Practical Implication
Primary Chiari I with symptomatic crowding or syringomyelia	Established anatomical disorder; EDS-specific prevalence and causation uncertain	Interpret tonsillar descent with symptoms, CSF-flow context, and competing explanations
Acquired tonsillar descent from spinal CSF loss	Established potential manifestation of SIH	Assess brain-sagging features and leak phenotype before labeling primary Chiari
Spontaneous spinal CSF leak/CSF–venous fistula	Established clinical entities with specialist diagnostic pathways; connective-tissue susceptibility supported observationally	Pursue targeted imaging when SIH phenotype is convincing, including after nondiagnostic first-line studies
Craniocervical instability attributed to hEDS	Plausible and reported in selected cohorts; imaging thresholds and intervention effectiveness not prospectively validated	Require clinicoradiographic concordance and avoid decisions based on isolated provocative measurements
Basilar invagination with neural compression	Established structural mechanism; EDS-specific causal attribution varies	Evaluate actual cervicomedullary compromise, not appearance alone
Symptomatic segmental spinal compression or deformity	Established neurological mechanisms; prevalence and EDS attribution depend on subtype	Localize objective myelopathy or radiculopathy before assigning cause
Tarlov cysts	Commonly incidental; symptomatic cases occur, EDS-specific association uncertain	Correlate level, symptoms, and neurological findings; do not infer causation from cyst presence
Classical tethered cord	Established anatomical and neurological disorder	Use clinical and imaging criteria appropriate to established dysraphism/tethering
Occult tethered cord with normal conus in hEDS	Controversial; selected biomechanical/surgical series and limited controlled pediatric evidence	Do not infer surgical efficacy or diagnosis from symptoms or uncontrolled outcomes
Adhesive arachnoidopathy caused by EDS	Arachnoidopathy is established; a specific causal EDS link is unproven	Investigate established causes and objective intradural findings

Note: Evidence descriptors are narrative categories, not formal GRADE ratings; they describe different claims (existence, EDS association, diagnosis, and treatment) and must not be interpreted as equivalent.

1.2. Distinct Contribution of This Perspective

Previous reviews have catalogued neurological and spinal manifestations reported in EDS [3,4,5]. Our contribution is not a new catalogue, a new syndrome, or a claim that connective-tissue pathology unifies disparate symptoms. It is a decision-oriented model that asks, in sequence, what neurological syndrome is present, which mechanism could plausibly generate it, what evidence would discriminate that mechanism from alternatives, and what findings should stop further structural escalation. We propose this framework as a testable clinical reasoning aid; it has not been prospectively evaluated for diagnostic performance or patient benefit.

2. The Structural Biology of the Nervous System

The neurological consequences of connective-tissue disorders are best understood by recognizing the extent to which neural function depends upon a mechanically stable extracellular environment. Neurons and glial cells do not function in isolation. The brain, spinal cord, and nerve roots are suspended, protected, perfused, and mechanically constrained by structures rich in collagen, elastin, proteoglycans, and other extracellular-matrix components.

The meninges provide one of the clearest examples, but their layers have different properties. The dura mater is a collagen-rich fibrous envelope that contributes tensile resistance and CSF containment. The arachnoid barrier and trabecular architecture help organize the CSF-filled subarachnoid compartment, whereas the pia closely invests neural tissue and accompanies vessels at the neural surface. These layers should not be treated as mechanically interchangeable; a dural leak, an arachnoid adhesion, and a pial abnormality would have different implications for neural function. Contemporary anatomy increasingly recognizes the meninges not as passive coverings but as structurally and biologically complex tissues containing fibroblasts, extracellular matrix, vascular and lymphatic networks, immune cells, and innervation [9].

Peripheral nerves likewise depend on connective-tissue compartments: endoneurium surrounds individual nerve fibres, perineurium forms a specialized fascicular barrier, and epineurium supports and protects nerve trunks. This organization illustrates a further distinction between structural susceptibility and demonstrable nerve injury. Connective tissue is equally fundamental to the spinal column. Intervertebral discs distribute compressive loads, while spinal ligaments constrain excessive translation and rotation and contribute to stability across highly mobile segments. This relationship is especially consequential at the craniocervical junction, where the occiput, atlas, and axis permit substantial physiological mobility while relying heavily upon ligamentous structures for stability. Mobility is necessary for normal function, but neural tissue remains vulnerable to the consequences of excessive or pathological motion.

The extracellular matrix provides another level of structural organization. Rather than functioning simply as inert scaffolding, extracellular-matrix components influence tissue mechanics, cellular adhesion, signaling, repair, and the transfer of mechanical forces between cells and their environment. Their composition and organization differ among tissues according to physiological demand. A connective-tissue abnormality may therefore have very different consequences in skin, a peripheral joint, the dura, or a ligament stabilizing the spinal cord and brainstem.

This distinction is particularly important in EDS. These syndromes are biologically heterogeneous, and their structural consequences vary by molecular subtype and tissue involved. Several spinal manifestations have been reported across EDS, but significant gaps remain in defining their prevalence, mechanisms, and optimal management [5]. The neurological relevance of connective-tissue disease therefore cannot be inferred from hypermobility alone.

Instead, the key concept is the mechanical context. Connective-tissue susceptibility becomes neurologically consequential when it alters a structure whose function is necessary to protect, stabilize, contain, or support neural tissue. Depending upon location, the resulting physiological disturbance may involve abnormal motion, compression, traction, altered load transmission, failure of CSF containment, disturbed CSF flow, or changes in relationships among neural and vascular structures.

Connective-tissue susceptibility provides the substrate; neurological dysfunction depends upon what that susceptibility does within a particular anatomical and mechanical environment.

3. From Hypermobility to Neurological Dysfunction

Joint hypermobility describes motion beyond the expected physiological range, but increased mobility alone does not establish pathological instability. Hypermobility may be asymptomatic, whereas instability implies failure of a joint or its supporting structures to maintain appropriate alignment and control under physiological loading. In connective-tissue disorders, ligamentous laxity may permit increased motion without necessarily producing neural compromise.

This distinction becomes particularly important in the spine. Unlike many peripheral joints, spinal motion occurs adjacent to the spinal cord, brainstem, nerve roots, vertebral arteries, and CSF spaces. The neurological consequence of instability therefore depends not simply upon how far a segment moves, but upon what that movement does to neighboring structures. Potential mechanisms include intermittent or sustained neural compression, deformation or traction of the spinal cord or brainstem, nerve-root irritation, altered vascular relationships, and disturbance of CSF flow.

Symptoms alone cannot reliably distinguish physiological mobility, hypermobility, and pathological instability. Headache, neck pain, dizziness, disequilibrium, paresthesias, fatigue, dysphagia, and autonomic symptoms are clinically important but nonspecific. Similarly, EDS or generalized joint hypermobility may increase the plausibility of a mechanical contribution without establishing one.

Imaging introduces another layer of complexity. Static studies characterize anatomy in a particular position, whereas a suspected mechanical disorder may theoretically manifest most clearly during movement or loading. Dynamic radiography, CT, and MRI have therefore been used in evaluation of suspected craniocervical instability. Proposed measurements include the clivo-axial angle, Harris measurement, Grabb-Mapstone-Oakes measurement, and angular displacement of C1 relative to C2. However, thresholds and diagnostic approaches vary across published studies, and these measurements have not been sufficiently prospectively validated in EDS populations to function as stand-alone diagnostic tests. A systematic review identified only 16 eligible studies, with evidence levels ranging from III to V [6,7].

This uncertainty should not be interpreted as evidence that pathological instability does not occur. Rather, it emphasizes clinicoradiographic concordance. The case for neurologically significant instability becomes stronger when a plausible structural abnormality corresponds with symptom behavior, objective neurological findings, and a reproducible mechanical mechanism.

A useful distinction can therefore guide the remainder of this discussion: hypermobility describes movement; instability describes mechanical failure; neurological disease requires consequence.

4. The Craniocervical Junction

The craniocervical junction (CCJ) represents a particularly important interface between connective-tissue mechanics and neurological function. Formed by the occiput, atlas, axis, and their supporting ligaments, the CCJ must accommodate substantial physiological movement while protecting the cervicomedullary junction, lower cranial nerves, upper cervical nerve roots, vertebrobasilar circulation, and CSF pathways.

Chiari I malformation, craniocervical instability (CCI), and basilar invagination may coexist in selected patients, but they represent distinct anatomical problems and should not be treated as interchangeable manifestations of connective-tissue disease.

4.1. Chiari I Malformation

Chiari I malformation (CMI) is characterized anatomically by caudal displacement of the cerebellar tonsils through the foramen magnum. Traditional models emphasize mismatch between the volume of the posterior cranial fossa and its neural contents, with crowding at the foramen magnum potentially disturbing CSF flow. Clinical significance, however, cannot be determined from tonsillar position alone. Tonsillar ectopia may be incidental, whereas symptomatic CMI can produce occipital or Valsalva-associated headache, brainstem or cerebellar symptoms, and, when CSF obstruction is substantial, syringomyelia.

CMI and low-lying cerebellar tonsils have been reported in patients with heritable connective-tissue disorders and may coexist with CCI, basilar invagination, or other craniocervical abnormalities [10,11]. Coexistence, however, does not establish a single causal pathway. Connective-tissue disease is better considered a potential modifier of craniocervical biomechanics in selected patients than a general explanation for CMI.

Recent referral-center data further illustrate the complexity of this overlap. In a retrospective cohort from a specialized connective-tissue neurology and neurosurgical center, Ruhoy and colleagues reported substantial co-occurrence of hEDS, Chiari I malformation, tethered cord syndrome, and procedures directed toward craniocervical instability. The authors emphasized that the cohort represented a severely affected referral population and should not be generalized to the broader hEDS population [12].

A second distinction is essential: primary Chiari I malformation should not be conflated with acquired cerebellar tonsillar descent caused by CSF-volume loss. Spontaneous intracranial hypotension may produce downward displacement of the brain and tonsils alongside other signs of brain sagging, including pachymeningeal enhancement, venous engorgement, and altered brainstem relationships. A history of orthostatic headache and a compatible constellation of imaging findings should prompt consideration of CSF leakage before labeling low-lying tonsils as primary Chiari or contemplating decompression [13,14,15,16,17]. No single imaging sign is definitive, and specialist neuroradiological interpretation is important [17].

Persistent symptoms following Chiari decompression similarly require careful reassessment rather than automatic attribution to either failed decompression or CCI. Depending upon the phenotype, evaluation may need to reconsider CSF obstruction, ventral brainstem relationships, instability, intracranial pressure disorders, and alternative headache etiologies.

4.2. Craniocervical Instability

CCI represents inadequate stabilization of the skull relative to the upper cervical spine. Because stability of the occiput-C1-C2 complex depends substantially upon ligamentous structures, hereditary connective-tissue disorders provide a biologically plausible substrate for excessive pathological motion. When sufficiently severe, abnormal translation or angulation may deform the brainstem or upper spinal cord, affect lower cranial nerves, alter CSF relationships, or contribute to findings described as cervicomedullary syndrome.

The central challenge is determining where physiological or hypermobile motion ends and pathological instability begins. Several radiographic measures have been proposed, but published thresholds and surgical criteria remain inconsistent. The available literature is dominated by retrospective cohorts and selected surgical series, and systematic review has found a lack of high-quality prospective evidence for evaluation and treatment of CCI in EDS [6,7].

A 2024 retrospective series of 53 highly selected patients with EDS, severe symptoms and neurological findings, radiographic CCI, and failed nonoperative management reported postoperative improvements in headache, neck pain, functional status, and several neurological symptoms [18]. Importantly, 32 patients underwent suboccipital decompression during the same operation, follow-up averaged 15.1 months, and four patients required reoperation for wound dehiscence. The study lacked a nonsurgical control group and cannot isolate the contribution of fusion from concurrent decompression, selection effects, natural history, rehabilitation, or other care. These findings are hypothesis-generating for selected patients, not proof that the proposed imaging thresholds establish a causal lesion or predict benefit in the broader hEDS population.

Response to fusion can support the relevance of a mechanical abnormality in a selected cohort, but surgical response cannot retroactively validate CCI as the explanation for similar symptoms in every patient with EDS.

4.3. Basilar Invagination and Ventral Brainstem Relationships

Basilar invagination refers to abnormal superior migration of the upper cervical spine, particularly the odontoid, toward the foramen magnum. Unlike CMI, which centers on caudal displacement of cerebellar tissue, basilar invagination reflects an abnormal relationship between the cranial base and upper cervical spine. When substantial, it may reduce the space available for the brainstem and upper spinal cord and contribute to ventral neural compression.

CMI, CCI, and basilar invagination may coexist because they involve structures within the same constrained anatomical region. The term complex Chiari has been used for presentations involving CMI together with abnormalities such as basilar invagination, ventral brainstem compression, kyphotic clivo-axial relationships, or instability [10,11]. Terminology, however, should not obscure the more important clinical question: which structural abnormality, if any, is producing a physiological consequence in the individual patient?

4.4. Anatomy Requires Clinical Context

The CCJ illustrates the central challenge of neurological connective-tissue disease. A patient may have tonsillar ectopia without symptomatic Chiari, hypermobility without CCI, or an unusual morphometric measurement without neurological compromise. Conversely, meaningful pathology may depend upon position and movement and may not always be fully represented by a single neutral, supine image.

Evaluation therefore requires integration of anatomy, biomechanics, symptom phenotype, neurological examination, and—when appropriately indicated—dynamic or physiologically relevant imaging. The relevant question is not simply whether the anatomy is unusual, but whether that anatomy changes the conditions under which the nervous system must function.

5. The Mobile Spine: Segmental Instability and Spinal Deformity

The same principles apply throughout the mobile spine. Each spinal segment must balance mobility with stability while protecting the spinal cord and nerve roots and transmitting mechanical loads across the vertebral column. Intervertebral discs, facet joints, ligamentous structures, paraspinal musculature, and vertebral alignment function together to maintain this balance.

Segmental instability may manifest as spondylolisthesis, retrolisthesis, lateral translation, or rotational displacement. In patients with ligamentous laxity, altered passive restraint may plausibly change the distribution of forces across discs and facet joints and increase reliance upon muscular stabilization. As at the CCJ, however, increased mobility should not automatically be interpreted as pathological instability. Clinical relevance depends upon whether abnormal mechanics produce pain, progressive deformity, neural compression, or another demonstrable functional consequence.

Spinal deformity provides a related but distinct mechanism. Scoliosis and kyphosis are recognized manifestations of several heritable connective-tissue disorders, although their prevalence and severity differ substantially among EDS subtypes. Certain molecularly defined subtypes, particularly kyphoscoliotic EDS, carry a well-established propensity for early and sometimes progressive spinal deformity; these observations should not be generalized directly to hEDS [1,5].

Neurological consequences are again determined by effect rather than appearance alone. Spinal cord compression may produce myelopathic findings including weakness, sensory disturbance, gait dysfunction, hyperreflexia, and bowel or bladder dysfunction, whereas nerve-root involvement may produce radicular pain, sensory loss, or focal weakness.

Degenerative disc disease, scoliosis, spondylolisthesis, and other spinal abnormalities are also common in the general population. Their presence in a patient with hEDS or generalized joint hypermobility does not establish connective-tissue disease as their cause.

Across the vertebral column, therefore, connective-tissue susceptibility may alter spinal mechanics, but neurological significance emerges when altered mechanics produce a meaningful consequence for neural function.

6. Meningeal Vulnerability and Cerebrospinal Fluid Disorders

Connective-tissue vulnerability may affect the nervous system through mechanisms other than joint instability. The meninges provide a structurally distinct but conceptually related interface: rather than controlling movement between bones, they maintain the physical compartments surrounding the brain and spinal cord and contribute to containment of CSF.

This relationship is particularly relevant to spontaneous intracranial hypotension (SIH), a neurological syndrome generally resulting from spinal CSF leakage. Contemporary classifications recognize several mechanisms, including ventral dural tears, lateral leaks associated with nerve-root sleeves or diverticula, and CSF-venous fistulas (CVFs), in which CSF passes directly into the venous system without necessarily producing an extradural fluid collection [13,14,15]. Recognition of CVFs has substantially changed the diagnostic approach to SIH, with specialized techniques such as lateral decubitus CT myelography and digital subtraction myelography capable of identifying fistulas that may be occult on conventional imaging [15,16].

Heritable connective-tissue disorders have repeatedly been reported among patients with spontaneous spinal CSF leakage, supporting the biological plausibility that altered dural integrity may increase susceptibility in selected patients [19]. The association should not be interpreted deterministically: connective-tissue disease may provide a susceptible substrate but is neither necessary nor sufficient for development of a spontaneous leak.

The neurological phenotype produced by CSF loss reflects the physiological consequences of altered intracranial CSF volume rather than the dural defect itself. Orthostatic headache is characteristic, but neck pain, nausea, tinnitus or hearing disturbance, dizziness, diplopia, and cognitive symptoms may also occur. Importantly, intracranial hypotension can be a misleading term because normal opening pressure does not exclude SIH, and brain MRI may occasionally be normal despite genuine disease [13,14]. SIH therefore illustrates an important principle: absence of a conventional static abnormality does not necessarily exclude a physiological disorder. However, the evidence supporting specialized leak-localization techniques in a patient with a convincing SIH phenotype cannot be transferred to provocative craniocervical imaging in hEDS, where normative thresholds, reproducibility, diagnostic accuracy, and treatment implications remain less established. These are separate diagnostic pathways, not parallel proofs of the same proposition.

Meningeal diverticula and perineural or Tarlov cysts introduce additional complexity. These abnormalities may reflect local differences in meningeal architecture, but their presence alone does not establish neurological disease. Tarlov cysts are commonly detected as incidental imaging findings, and only a minority appear to correspond with clinical symptoms; a meta-analysis of 13,266 subjects found that 15.6% of identified cysts corresponded with symptoms [20]. Their occurrence in EDS has been reported, but the magnitude and specificity of the association remain incompletely defined [5].

These disorders should also not be collapsed into a generic “CSF problem.” A ventral dural tear, CSF-venous fistula, meningeal diverticulum, and symptomatic perineural cyst represent anatomically and physiologically different abnormalities. Similarly, headache in a patient with hEDS may reflect migraine, cervicogenic mechanisms, Chiari-related CSF obstruction, SIH, another intracranial pressure disorder, or an unrelated cause.

For neurologists, the practical implication is that symptoms suggestive of altered CSF dynamics—particularly a reproducible relationship to posture—should prompt consideration of a CSF disorder even when initial testing is nondiagnostic. Investigation should then be driven by the suspected mechanism rather than connective-tissue status alone.

At a joint, connective-tissue vulnerability may permit pathological movement; at the dura, it may impair compartmental integrity. For CSF disorders, the critical transition is from meningeal susceptibility to failure of containment and disruption of the physiological environment required for normal neural function.

7. Tethering and Arachnoid Pathology

Connective-tissue abnormalities may also become neurologically consequential through traction and intradural restriction. Tethered cord syndrome (TCS) and adhesive arachnoid pathology illustrate these mechanisms, although the strength of evidence linking each to heritable connective-tissue disorders differs substantially.

7.1. Tethered Cord Syndrome

TCS describes neurological dysfunction resulting from pathological fixation of the spinal cord and consequent abnormal traction. Classical causes include a thickened or fatty filum terminale, spinal lipoma, split-cord malformation, and postoperative adhesions associated with spinal dysraphism. Clinical manifestations may include lumbosacral pain, lower-extremity weakness or sensory disturbance, gait abnormalities, and bowel or bladder dysfunction. Conventional imaging may demonstrate a low-lying conus medullaris or abnormal filum terminale [21,22].

The concept of occult tethered cord syndrome (OTCS) is more controversial. OTCS describes a tethered-cord phenotype despite a normally positioned conus and absence of conventional radiographic findings. Diagnostic criteria and indications for surgery remain unsettled [23,24].

A potential biological link to hEDS has nevertheless emerged. A 2022 study examined filum terminale tissue and biomechanical properties in 78 surgically selected patients classified as having radiographically occult hEDS-associated TCS and compared them with patients undergoing surgery for conventional TCS. Investigators reported collagen fibril abnormalities and altered biomechanical properties and proposed that abnormal filum mechanics might transmit pathological stretch forces despite normal conus position [25].

These findings provide an intriguing biomechanical hypothesis but do not establish prevalence, validated diagnostic criteria, or the effectiveness of surgery in the broader hEDS population. Countervailing controlled evidence must also be considered: a randomized pilot trial of 21 children with urinary symptoms, normal conus position, and abnormal urodynamics found no statistically significant differences in urological outcomes between medical management and medical management plus filum section [26]. The trial was small, underpowered for modest effects, and conducted in children rather than adults with hEDS. It neither establishes equivalence nor resolves the hEDS-specific question, but it demonstrates why improvement in uncontrolled surgical cohorts cannot be assumed to establish surgical efficacy. More recent literature describing co-occurrence of tethering and cervical instability further develops the proposed clinical framework but remains based largely on selected populations and observational experience [27].

Accordingly, a normal conus position should not by itself prove or disprove a traction-based neurological disorder, but neither should compatible symptoms alone establish occult tethered cord syndrome.

7.2. Adhesive Arachnoid Pathology

Spinal adhesive arachnoidopathy represents a different form of intradural disturbance. Chronic inflammation and fibrosis within the arachnoid may produce adhesions among nerve roots, meninges, and other structures within the spinal canal, potentially disrupting neural mobility and CSF flow. Clinical manifestations are heterogeneous and may include neuropathic pain, sensory disturbance, weakness, and other neurological deficits.

A specific relationship between EDS and adhesive arachnoid pathology, however, remains insufficiently established. A 2024 systematic review encompassing 176 studies and 510 reported patients identified trauma, infection, surgery, hemorrhage, and other etiologies but did not establish heritable connective-tissue disease as a major cause [28]. A role for connective-tissue biology in arachnoid vulnerability remains possible but should presently be regarded as a hypothesis rather than an established association.

The distinction illustrates the importance of preserving different evidence levels within the same clinical framework. Classical tethered cord has established anatomical substrates; occult tethering in hEDS has emerging biomechanical evidence but unresolved diagnostic criteria; and a causal relationship between EDS and adhesive arachnoid pathology remains insufficiently demonstrated.

8. Applying a Proposed Clinical Reasoning Framework

The proposed sequence—neurological phenotype → plausible mechanism → concordant anatomy or physiology—begins with history, examination, and the ordinary neurological differential diagnosis. Connective-tissue phenotype modifies pretest probability but cannot itself localize pathology. The clinician should first identify objective deficits or characteristic symptom signatures, then select tests that discriminate among mechanisms, and finally assess whether any abnormality actually explains the phenotype. Alternative diagnoses and discordant results are active decision points, not obstacles to be overcome by increasingly provocative imaging. This framework is conceptual and has not been validated for sensitivity, specificity, clinical utility, or effects on patient outcomes.

8.1. Illustrative Presentation A: A Structural Investigation Is Justified

Consider an adult with a confirmed hypermobility disorder who develops a new, clearly orthostatic headache that improves substantially when supine, accompanied by neck pain and auditory symptoms. The dominant phenotype is posture-dependent headache, not generalized joint laxity. The leading physiological question is whether spinal CSF loss has altered intracranial CSF volume. Brain MRI with and without contrast and appropriate spinal imaging may identify supportive findings, but normal opening pressure or a nondiagnostic first MRI does not exclude SIH [13,14,15,16]. When clinical suspicion remains high, a specialist CSF-leak service may select further imaging according to the suspected leak mechanism, including consideration of a CSF–venous fistula. Findings such as a compatible brain-sagging pattern, extradural CSF, or a localized fistula strengthen a structural explanation; a stable migraine phenotype, absent postural dependence, or an alternative explanation may lower suspicion. Low-lying tonsils in this context should prompt assessment for acquired descent before primary Chiari decompression is considered. Specialist-directed escalation is justified by a specific syndrome and a testable mechanism—not by hEDS alone.

8.2. Illustrative Presentation B: Structural Escalation Is Not Justified

Consider an adult with hEDS, chronic neck pain, episodic dizziness, photophobia, nausea, and fatigue, but no progressive focal neurological deficit, no reproducible signs of myelopathy or lower cranial nerve dysfunction, and no established instability on appropriately interpreted standard imaging. Symptoms cluster around migraine episodes and upright tachycardia; examination and orthostatic measurements support targeted headache and autonomic assessment. A borderline craniocervical measurement or symptom provocation during neck movement would not independently establish CCI. Here, management should prioritize evidence-based evaluation and treatment of the better-supported syndromes, rehabilitation where appropriate, and reassessment for genuinely new objective deficits. Additional dynamic imaging is not justified solely by persistent symptoms, hypermobility, or an isolated nonvalidated measurement. These scenarios are illustrative composites, not patient data or validated decision rules.

8.3. How to Handle Discordance and Uncertainty

Concordant findings are strongest when a plausible lesion, characteristic phenotype, objective examination, and validated test agree. Discordance should trigger review of imaging quality and interpretation, consideration of incidental findings, and renewed differential diagnosis. For suspected SIH, high clinical suspicion can warrant specialist review despite negative first-line testing because this limitation is established in the literature. For suspected CCI in hEDS, uncertainty about provocative imaging thresholds should not automatically lead to repeated imaging or fusion. New progressive weakness, myelopathy, objective cranial neuropathy, or bowel/bladder neurological deficits warrant prompt reassessment; nonspecific symptom persistence without new objective findings does not, by itself, justify invasive investigation.

9. Evidence Strength and the Framework’s Contribution

Table 1 summarizes the distinction between an established neurological disorder, evidence of its association with connective-tissue conditions, and evidence that a proposed intervention improves outcomes. These are separate questions. A condition can have a well-established anatomical mechanism while its increased frequency in hEDS remains uncertain. Conversely, a selected surgical cohort can report improvement without proving the selection criteria or the causal mechanism.

The novelty of the framework lies in explicitly separating these evidentiary steps and introducing stopping rules: if a structural finding lacks clinical concordance, or a better-supported nonstructural explanation accounts for the phenotype, further structural escalation may offer more risk than diagnostic benefit. Its utility should be tested prospectively against usual care, including diagnostic yield, unnecessary testing, patient-reported outcomes, functional outcomes, adverse events, and downstream procedures.

10. Research Priorities and Conclusions

The neurological consequences of connective-tissue disorders occupy an unusual position between established anatomy, compelling clinical observation, and an evidence base that remains uneven. The biological premise is straightforward: connective tissue contributes to the integrity of the meninges, spinal ligaments, intervertebral discs, vascular interfaces, and other tissues that protect and support the nervous system. What remains more difficult to establish is when vulnerability within these tissues crosses the threshold into clinically meaningful neurological disease.

Several priorities should guide future investigation, including prospective validation of the proposed reasoning framework itself. First, the field requires better characterization of connective-tissue phenotypes. EDS comprises biologically distinct disorders, and hEDS remains particularly heterogeneous. Studies that group molecularly defined EDS subtypes, hEDS, generalized joint hypermobility, and hypermobility spectrum disorders together may obscure disease-specific mechanisms. Improved molecular characterization and phenotyping may ultimately identify subgroups with different susceptibility to meningeal, ligamentous, or other neurological complications [1,2].

Second, suspected dynamic disorders require prospective validation of diagnostic methods. This is particularly apparent in CCI, where radiographic measurements and surgical criteria remain inconsistent and much of the evidence derives from retrospective or highly selected cohorts. Future studies should include appropriate asymptomatic and hypermobile comparison groups, standardized imaging protocols, objective neurological outcomes, and longitudinal follow-up [6,7,18].

Third, structural abnormalities must be connected more rigorously to physiological consequence and clinical phenotype. Advances in CSF-leak medicine illustrate the value of mechanism-specific investigation. Recognition of ventral dural tears, leaking diverticula, and CSF-venous fistulas has moved the field toward localization of distinct physiological mechanisms rather than reliance upon a single measurement such as opening pressure [13,14,15,16]. Similar progress elsewhere will require integration of symptom behavior, neurological examination, quantitative imaging, biomechanics, and longitudinal outcomes.

Finally, therapeutic evidence must evolve alongside diagnostic evidence. Prospective natural-history studies and controlled comparisons of conservative and operative approaches are particularly needed for CCI and proposed occult tethered cord in hEDS. Outcomes from carefully selected surgical populations can generate important evidence but cannot independently establish diagnostic criteria or determine which broader populations are likely to benefit [18,22,24,25,27].

The purpose of this research should not be to prove that connective-tissue disorders explain an expanding range of neurological symptoms. It should be to determine which patients have a neurologically meaningful structural or physiological consequence of connective-tissue vulnerability, through which mechanism, and how that consequence can be demonstrated objectively.

Connective tissue is integral to the environment in which the nervous system functions. Its vulnerability may manifest through instability, compression, traction, altered CSF containment or flow, and other mechanical or physiological disturbances. Yet susceptibility alone is not disease, anatomical variation alone is not dysfunction, and association alone is not causation.

For the neurologist, the challenge is one of integration: to recognize structural disease without over-attributing symptoms to it, to recognize dynamic physiology without abandoning objective evidence, and to remain open to emerging mechanisms while acknowledging where evidence remains incomplete.

When does connective-tissue vulnerability become neurological disease?

Answering that question—not simply identifying more structural abnormalities—should define the next phase of connective-tissue neurology.