Central Pain Syndrome with Manifestations in the Foot

To the Editor:

With increased life expectancies, improvements in medical technology, and the advent of new drugs, podiatric physicians are seeing and treating more patients with residual complications of stroke. One of the complications that will be increasingly encountered is central poststroke pain.

As defined by the International Association for the Study of Pain, central pain refers to pain resulting from damage to the central nervous system [1]. Central pain can result from lesions at any site in the brain and from any pathology. The greatest number of patients with brain lesions suffer from strokes. The incidence of central pain following stroke is 1 in 15,000. Central pain resulting from a stroke is often mistakenly referred to as thalamic pain, but in many patients with central poststroke pain the thalamus is not affected. Central pain has been shown to occur following lower-brainstem, thalamic, and suprathalamic cerebrovascular events. When the thalamus is involved, the lesion most often involves the posterolateral or posterior portion [2].

Central pain was first described in the literature in 1883 by Grieff [3], who reported on a patient who had suffered a cerebrovascular lesion. In 1906, Dejerine and Roussy [4] focused attention on central pain and coined the terms “thalamic pain syndrome” and “Dejerine-Roussy syndrome” to describe stroke-induced thalamic damage. They reported on a group of patients who had suffered strokes with residual slight hemiplegia, hemianalgesia or hemihypalgesia, hemiataxia, astereognosis, and sometimes choreoathetosis, all affecting the side of the body contralateral to the stroke site. The onset of pain after the stroke was often delayed for weeks to months and occurred spontaneously [2].

The pathophysiology of central pain remains unknown. Many authors have addressed the subject, with the most widely accepted explanation being the loss of inhibitory influences on somatosensory pathways of systems; however, the mechanism of this action remains controversial. Central pain also involves an abnormality in sensibility secondary to damage to the spinothalamic tracts, the thalamus, or the thalamocortical projection fibers. The dorsal column medial lemniscus pathways and wide-dynamic-range neurons are usually involved in a modifying role [2,5,6,7,8].

Central pain may manifest with unpleasant sensory changes that correspond with all or part of the territory in which somatosensory loss occurs. The onset of pain can be delayed for years after the causative event, and the pain may change in distribution and quality. The pain has been described as a burning sensation, an unpleasant tingling, “pins and needles,” and numbness. It has also been described as ripping, tearing, pressing, or twisting [2,9]. The pain is usually constant and often exacerbated by physical activity, mental stress, loud noises, and changes in the weather. It may be accompanied by somatosensory stimuli including hyperesthesia, hyperpathia, and allodynia. Patients may demonstrate features suggesting sympathetically maintained pain, including altered texture, color, and temperature of the skin [2,9]. None of the descriptions above is pathognomonic for central pain.

Case Report

A 50-year-old white man presented to the podiatric medical clinic at the Audie L. Murphy Veterans Administration Hospital in San Antonio, Texas, with a chief complaint of pain in the right foot of 4.5 years’ duration. The patient described the pain as aching in nature and constant, although worse during ambulation. He stated that he had learned to live with it over the years.

The patient’s initial symptoms appeared after he suffered a left thalamic stroke with residual right hemiparesis in December 1990. He stated that the pain in his foot had remained the same, with no increase or decrease in severity since the initial onset. He denied any alleviating or aggravating factors. After further discussion, the patient mentioned that his pain was not limited to the foot but was in fact present on the entire right side of his body, including the right side of his face. The pain experienced in the right upper extremity was identical to the pain in the right foot. Prior treatments included capsaicin .025%, amitriptyline, carbamazepine, ibuprofen, a metatarsal pad, a forefoot-padded ankle-foot orthosis, and transcutaneous electrical nerve stimulation.

The patient’s medical history was significant for a left hemorrhagic thalamic stroke, hypertension, degenerative joint disease of the cervical spine, alcoholism, and hiatal hernia. Physical examination revealed absent sharp/dull discrimination and proprioception on the entire right side. Muscle strength was 2/5 in the right upper extremity and 3/5 in the lower extremity. The patient had hyperreflexia and clonus on the right side. Myalgias were also present in all major muscle groups on the right side.

Magnetic resonance imaging of the head in 1990 showed extensive hemorrhaging on the left cerebral peduncle into the left lateral ventricle. Electrodiagnostic studies revealed no evidence of thoracic radiculopathy. A bone scan of the right hand and foot was performed and was not suggestive of reflex sympathetic dystrophy.

Discussion

Pain is not a commonly recognized symptom of cerebrovascular disease. Awareness of this entity and a thorough history and physical examination are crucial for a correct diagnosis. Patients who present with a history of a stroke accompanied by pain on the hemiplegic side should raise the clinician’s suspicion for central pain. Because of the thalamic infarct, involvement of the entire right side, and an unremarkable bone scan, reflex sympathetic dystrophy was ruled out in this case. The patient was referred to a pain clinic for proper management.

Currently, there is no universally effective therapy for central pain syndrome, making treatment of this condition difficult. Disability must be assessed according to the condition’s interference with the ability to work, to enjoy recreation, and to sleep. The treatment plan should begin with the simplest measures and progress to more complex measures, and should be a multidisciplinary approach. The physician must keep the patient and family informed of the risks, limitations, and chances of success of each treatment modality considered. Because no pain therapy is 100% effective, any mild improvement may be considered a significant achievement in treating this condition [2,9,10].

Avoidance of noxious stimuli is the mainstay of treatment [2]. This includes prevention and treatment of infection, spasticity, contracture, bowel and bladder complications, and pressure sores. The first medical treatment approach should include the use of antidepressants, which have an effect that is probably secondary to norepinephrine and serotonergic action. The therapeutic window is related to individual metabolism. Amitriptyline is the most commonly used agent, and dosage is usually 50 to 100 mg per day [2]. Tricyclic compounds have both primary analgesic properties and the ability to potentiate opiate anesthesia [11]. Most tricyclics have a low affinity for opiate receptors, and most produce analgesia that is not reversed by naloxone hydrochloride [12]. The mechanism by which tricyclics relieve pain is unknown; however, they bind to receptors of several neurotransmitters as well as block monoamine uptake [11,12]. Their major effect is probably due to inhibition of serotonin reuptake [13]. Antiepileptic agents work by means of suppression or enhanced inhibition of pathologic neuron firing. Phenytoin and carbamazepine inactivate sodium channels. Clonazepam, valproic acid, barbiturate, and gabapentin, all of which are minimally effective in reducing pain, enhance inhibition through γ-aminobutyric acid activation [2,14]. Narcotics and nonnarcotic analgesics do not provide adequate pain relief [1]. Local anesthetics utilize a mechanism similar to that of antiepileptic drugs, closing sodium channels and decreasing firing of abnormal, hypersensitive neurons. Other medications that have been tried include adrenergic agents, cholinergic agents, u receptor antagonist, and neuroleptics, but these have not provided adequate pain relief [2].

Other treatments include neuromodulation, which depends on the dorsal column medial lemniscus pathways being intact. Transcutaneous electrical nerve stimulation has been effective in some patients; spinal-cord stimulation has demonstrated poor efficacy; and deep brain stimulation has shown mixed results [2,15,16]. Sympathetic blockade in the form of stellate ganglion and lumbar sympathetic blocks with local anesthetics or local venous guanethidine blocks may provide some temporary pain relief [2,17]. A variety of operative treatments have been tried for central pain syndrome. These include cordotomy, cordectomy, dorsal root entry-zone lesions, rhizotomy, and intracranial surgeries including tractomy, thalamotomy, cingulotomy, and cortical ablation. The neurologic ablative procedures have demonstrated a 25% effectiveness in permanently relieving central pain states but are associated with a significant risk of brain injury [1,14,18].

Conclusion

Central pain syndrome has been described in order to raise the clinician’s level of suspicion for this entity. When evaluating a patient with stroke or any other brain lesion, central pain should be included in the differential diagnosis. Although there are no strict and successful guidelines for treatment, proper and early diagnosis will at least make the patient and family aware of the underlying problem and enable the clinician to propose a treatment plan.