Black Hairy Tongue Syndrome: Case Report and Review of the Literature

Abstract

Background/Objectives: Black hairy tongue syndrome (BHT) is characterized by structural epithelial changes and a dark discoloration on the surface of the tongue, causing a variety of symptoms such as xerostomia, altered taste, and nausea. Methods: Herein, we report a 70-year-old female patient with a history of Sjogren’s syndrome, rheumatoid arthritis, and occasional use of intranasal and inhaled corticosteroids, who presented with BHT exacerbated by consumption of colored beverages and carbohydrates. We also provide a review of the literature on published articles reporting cases of BHT syndrome. Results: Our patient’s condition improved after implementing dietary restrictions in combination with local care. A literature review revealed that the most common reported exposures and underlying conditions in patients with BHT were the recent administration of antibiotics, solid organ or hematologic malignancy, immunosuppressants, smoking, corticosteroids, autoimmune conditions, receipt of antidepressants, local radiation therapy, proton pump inhibitors, and alcohol. The majority of cases were successfully managed with the elimination of implicated factors when possible and local hygiene. Conclusions: Different factors may contribute to the development of BHT. Discontinuation of implicated medications together with measures for topical care constitute the most effective ways to achieve resolution.

1. Introduction

Black hairy tongue (BHT) syndrome, also known as black tongue syndrome, black hairy tongue, or lingua villosa nigra, is a benign and temporary condition characterized by a dark discoloration and elongation of the papillae on the surface of the tongue. Despite its alarming appearance, BHT is generally a benign and harmless condition, and most patients seek medical attention for esthetic reasons [1]. However, investigation for predisposing factors is necessary, as on certain occasions it might suggest a serious underlying pathology, such as malignancy [2]. In many cases, various symptoms have been reported, such as altered or metallic taste, foreign body sensation, burning mouth, xerostomia, nausea, or gagging [1,3].

Despite the name “black hairy tongue syndrome”, which may suggest that the tongue is completely black, in reality, the discoloration may vary in color. Thus, the appearance of the tongue can range from black to brown, yellow, green, or even white. The specific color depends on various factors, such as the underlying cause, oral hygiene, and the substances that come into contact with the tongue, which might account for said discoloration [3].

1.1. Pathogenesis

BHT primarily develops over the dorsal part of the tongue, which is covered by both non-keratinized squamous epithelial cells and fully keratinized epithelial cells, as well as filiform papillae. Filiform lingual papillae are small protrusions of the dorsal mucosa, surrounded by numerous threadlike projections termed secondary papillae. Filiform papillae serve to increase friction between the tongue and food and other particles within the oral cavity [3].

BHT is defined by two components: elongation of filiform papillae and discoloration of the dorsal tongue. Defective desquamation promotes hyperkeratosis of the tip of the filiform papillae and retention of the secondary papillae, leading to their elongation and giving them a hair-like appearance [1,4]. It is hypothesized that conditions that decrease tongue movement or affect friction may cause elongation of the papillae [5]. These changes provide a suitable environment for further changes, each of which can affect the pigmentation of the tongue: entrapment of particles and debris from orally ingested substances (food, drinks, tobacco), overgrowth of chromogenic bacteria and fungi, production of bacterial porphyrins, which lead to discoloration, and changes in local pH [3]. Antimicrobial use may promote bacterial growth, fungal growth, or even cause discoloration directly [5].

1.2. Epidemiology-Causes

The actual frequency of BHT syndrome is difficult to estimate, as it largely depends on population characteristics and interobserver variability. In addition, the majority of cases described in the literature consist of single case reports or small case series. Nevertheless, several factors have been identified that increase the risk of BHT, although evidence is primarily based on individual case reports or small case series. Of note, a matched case–control study of 672 patients identified a higher risk for hairy or coated tongue among elderly patients, men, smokers, and patients with chronic medical conditions [6]. Possible causes of dark tongue discoloration can be classified in broad categories as follows:

1.2.1. Poor Oral Hygiene

Poor oral hygiene is a common factor in the development of BHT. Infrequent, improper, or bad oral hygiene practices can lead to the accumulation of bacteria, food debris, and dead cells on the surface of the tongue. This, in turn, promotes the growth of microorganisms, disrupting normal shedding of cells and leading to elongation of the papillae. On the other hand, prolonged or excessive use of oxidizing mouthwashes (e.g., containing sodium peroxide and hydrogen peroxide) has also been associated with BHT [7].

1.2.2. Dry Mouth

Factors associated with decreased production of saliva and dry mouth (xerostomia), such as Sjögren’s syndrome and various medications, although not directly associated with BHT, can impede normal oral function and defensive mechanisms, leading to dental decay, oral candidiasis, and other oral infections. Decreased saliva can lead to alterations in the oral microbial balance, which could potentially contribute to the development of conditions such as BHT.

1.2.3. Tobacco Use

Smoking or chewing tobacco is reported to have a strong association with the development of BHT. Various chemicals contained in tobacco can alter the oral bacterial flora and affect the normal shedding of cells. Additionally, the heat and smoke from tobacco can further irritate and discolor the tongue’s surface [1].

1.2.4. Frequent Consumption of Certain Foods and/or Beverages

Consumption of certain substances, such as coffee, tea (particularly black tea), red wine, and certain mouthwashes that contain oxidizing agents, can stain the tongue papillae, contributing to discoloration. These substances increase the risk of discoloration in patients who have predisposing factors, such as poor oral hygiene [1].

1.2.5. Antibiotics and Other Medications

Antibiotics disrupt the normal flora of the mouth and tongue, thus allowing other bacteria or fungi to overgrow and lead to infections (such as oral candidiasis) or disrupt the normal oral function. Antibiotics most commonly reported in patients with BHT include tetracyclines, b-lactams, cephalosporins, and linezolid [5]. Other medications, such as bismuth-containing compounds, can affect the normal shedding of cells on the tongue’s surface and lead to discoloration.

1.2.6. Immune Suppression

Although there is no direct evidence to suggest that immune suppression directly increases the risk of BHT, individuals with compromised immune systems, such as those who are undergoing chemotherapy, organ transplant recipients, or people with HIV/AIDS, may have a higher susceptibility to various oral health issues, including infections, fungal overgrowth, and side effects due to medications [1]. In such cases, the immune system’s ability to maintain the oral microbial balance may be compromised, which could potentially contribute to the development of BHT. Additionally, while not specific to BHT, some immunosuppressive agents and biologic agents have been associated with oral health issues in general, potentially leading to an increased risk of oral complications. Such examples are corticosteroids, other immunosuppressing medications such as cyclosporine, methotrexate, and mycophenolate mofetil, which may increase the risk of oral infections, including fungal infections, or contribute to the development of other oral conditions. Biologic agents, used for the treatment of autoimmune conditions, can also affect the host’s immune response.

1.2.7. Individual Risk

Despite the above, it is worth noting that some individuals may be more prone to the condition due to individual differences in oral flora, saliva composition, or other undocumented factors that influence tongue health.

1.3. Management

It is very important to reassure the patient that BHT is a benign condition and is often self-limiting with a good prognosis. Management primarily involves improving oral hygiene practices, identifying and modifying, or entirely removing causative medications if possible, and addressing any underlying causes. In most cases, the condition resolves on its own with proper care. However, there are certain medications that may be used in specific situations or if the condition persists. These include:

• Mouth rinses and light scraping with diluted hydrogen peroxide or other antiseptic agents. These rinses can help reduce the bacterial load and remove the hyperkeratotic papillae. Care is necessary, as excessive use of local agents can cause oral irritation, damage to oral tissues, or disturbance in the natural oral microbial balance [7].
• Topical antifungals. In some cases, topical antifungal medications may be used if an overgrowth of fungi, such as Candida, is suspected or confirmed. However, it should be noted that only a small proportion of cases are directly associated with fungal infection.
• Other medications. In rare instances where other measures have been unsuccessful or the condition is persistent, other medications may be considered. Reported options include topical or oral retinoids, topical triamcinolone, and topical keratinolytics [1,4].

Medical treatment for BHT is typically reserved for severe or persistent cases. The primary focus is on improving and maintaining good oral hygiene practices and addressing underlying factors.

The aim of the current study is to present a case of BHT in a 70-year-old female patient and to review relevant evidence in the literature.

2. Case Presentation

A 70-year-old female presented with a 1-year history of persistent tongue discoloration accompanied by dysgeusia and dry mouth. She characterized dysgeusia as a continuous bitter taste in her mouth, which affected her appetite, subsequently leading to a reported loss of weight. Her past medical history was remarkable for chronic smoking up to 5 years ago (40 pack-years), rheumatoid arthritis, and Sjogren’s syndrome under tocilizumab (an anti-IL6 agent) for the past year, chronic asthma, and allergic rhinitis with occasional use of inhaled and intranasal corticosteroids. For her tongue condition, she had previously received a regimen of topical miconazole for probable fungal infection, with no improvement.

Upon examination, the dorsal tongue had obvious yellow-brown discoloration. The remaining physical examination was normal. Given her history of Sjogren’s syndrome, an ultrasonography of the thyroid and cervical region was performed to rule out conditions that might be related to oral infestation, with no abnormal findings. General laboratory results (full blood count, biochemistry, inflammation markers) were normal.

She was initially treated with oral fluconazole for 14 days and with a recommendation for local hygiene with mild mouthwash rinses but no scraping, with no improvement. Upon re-examination, further investigation with laryngoscopy was decided to rule out deep-seated fungal infection or other conditions that might have affected the oral cavity. Laryngoscopy revealed stomatitis and tongue discoloration, but no evidence of fungal infection or other abnormalities. A throat swab culture revealed β-hemolytic streptococcus, for which she received cefuroxime for 1 week. Due to the absence of anatomical abnormalities, no histology was performed.

Two months after initial presentation, follow-up examination confirmed persistence of the tongue discoloration and associated symptoms of dry mouth and dysgeusia. Further questioning revealed that her condition was exacerbated after the consumption of carbohydrates. In addition, the patient admitted to ingesting quantities of colored beverages and black tea.

Therefore, the patient was recommended to stop ingesting colored beverages and black tea, whereas a low-carbohydrate diet was recommended, primarily to avoid sweets, sugar, and high-starch foods such as flour-based products. She was also instructed to perform local cleansing with mild tongue scraping, diluted hydrogen peroxide twice daily for 5 days.

Two weeks later, upon re-evaluation, the discoloration of the tongue had subsided. However, dry mouth and dysgeusia persisted, a finding which could also be due to her existing Sjogren syndrome. In the following months, she reported occasional recurrences of dark discoloration of the tongue, but these were related to previous consumption of colored beverages and carbohydrates. She followed instructions for local hygiene and light scraping, with improvement.

One year after her initial presentation and two years after the condition first appeared, the patient reports significant improvement but not complete resolution.

3. Discussion

We present a case of BHT syndrome in an elderly woman with several possible contributors, including an underlying autoimmune condition affecting the oral mucosa, administration of an immune-modifying agent, chronic tobacco smoking, and receipt of local corticosteroids. All these factors have been previously associated with the pathogenesis of BHT through different mechanisms. Therefore, it is difficult to implicate any individual factor. In fact, following careful observation of our patient’s course, there are two possible contributing factors to the development of her condition: chronic dry mouth due to Sjogren’s syndrome, which affects the local epithelium, and discoloration due to specific foods and beverages, thus supporting the necessity of an individualized approach and management. In addition, BHT should not be considered a mere aesthetic condition, as its clinical manifestations may have a significant burden on the patient’s quality of life. To this end, our patient reported weight loss, as her taste disturbance and xerostomia limited her ability to enjoy food.

In line with our case, a literature review identified the above-mentioned conditions as potentially contributing to BHT, whereas in the majority of published cases, more than one factor is recognized as possibly associated with the development of BHT [8,9,10,11,12,13,14,15].

Table 1. Reported case series of patients with black hairy tongue syndrome.

First Author, Year	Cases (n)	Presentation	Comorbidities	Exposures	Culture Results	Treatment	Resolution
Bedford P.D., 1946 [8]	2	Sore throat, dry cough, hoarseness, malaise	NA	Tobacco smoking Penicillin topical	NA	None	Resolution
Wolfson S.A., 1949 [9]	4	Tongue discoloration, Bronchitis	NA	Penicillin topical and systemic	Candida spp. (1 case)	Penicillin discontinued, Mouth rinses	Resolution
Langtry J.A., 1992 [10]	3	Tongue discoloration, Dysgeusia	Cystitis 6+ months ago	Tobacco smoking Antibiotics	NA	Nystatin suspension, Miconazole oral gel, Hexetidine mouthwash, Topical tretinoin 0.025%	Resolution
Greco S., 1997 [11]	3	Glossitis with associated black tongue	Helicobacter pylori infection, peptic ulcer disease	Lansoprazole (60 mg/d) Clarithromycin (1 g/d)	NA	Antibiotic treatment discontinued	Resolution
Akay B.N., 2010 [12]	15	Xerostomia	AML, NHL, Primary myelofibrosis, ALL, HL, MDS, CLL	Bu-Cy, CsA, MTX SCT, MMF, sertraline, TMP-SMX, UDCA	Negative	NA	NA
Kannan S., 2014 [13]	5	Asymptomatic	Edentulism	Tobacco smoking	NA	Dentures	Improvement
Jain A.K., 2017 [14]	2	Tongue discoloration	TB infection	Injection capreomycin, cycloserine, moxifloxacin, linezolid, ethionamide, PAS	NA	Linezolid withheld, Tongue brushing	Resolution
Yamagishi Y., 2017 [15]	5	Paresis of left limb	Reflux esophagitis, DM, Malignant brain tumor	Radiotherapy, Corticosteroids, MTX	C. albicans (2 cases)	Tongue brushing	Improvement

ALL; acute lymphoblastic leukemia, AML; acute myeloid leukemia, Bu; busulphan, CLL; chronic lymphocytic leukemia, CML; chronic myelogenous leukemia, CsA; cyclosporine, Cy; cyclophosphamide, DM; diabetes mellitus, HL; Hodgkin lymphoma, MDS; myelodysplastic syndrome, MMF; mycophenolate mophetil, MTX; methotrexate, Mel; melphalan, NA: not available, NHL; non-Hodgkin lymphoma, SCT; stem cell transplant, TB; tuberculosis, TMP-SMX; trimethoprim-sulphametoxazole, UDCA; ursodeoxycholic acid.

summarizes the case series of BHT published in the literature. Previous reports have described solid organ or hematologic malignancy as the most common underlying conditions in patients with BHT. The most commonly reported exposures with possible association with BHT were recent administration of antibiotics (topical oral, oral, intravenous), immunosuppressive treatment, tobacco smoking, corticosteroids, antidepressants and/or antipsychotics, local radiation therapy, proton pump inhibitors, and chronic alcohol use. Among antibiotics, frequently reported groups were b-lactams, linezolid, trimethoprim/sulphamethoxazole, fluoroquinolones, and macrolides.

It is important to emphasize that the largest proportion of evidence from the literature on BHT is derived from case reports and small case series. Therefore, an analysis was not directed towards elucidating risk factors for BHT. However, the above-reported conditions confirm the different pathophysiologic hypotheses associated with local alterations of the oral epithelium and homeostasis, which can lead to the structural and phenotypical presentation of BHT. Specifically, solid organ and hematologic malignancies can affect the oral epithelial structure and function, either directly or indirectly through the effects of chemotherapy, immunotherapy, radiation, and surgery, thus increasing the risk for tongue alterations. In fact, immunosuppressive therapy and local radiation have indeed been previously reported [12,15]. On the other hand, autoimmune conditions, which were also reported in previous studies [16,17,18,19,20], raise the suspicion that tongue alterations, such as in BHT, can be either directly related to autoimmune disease effects or due to immune-modifying treatment.

To this end, our patient had two underlying autoimmune conditions: Sjogren’s syndrome and rheumatoid arthritis. It is our belief that chronic xerostomia (dry mouth) due to Sjogren’s syndrome represents the main substrate for the development of BHT, as the dry and friable oral mucosa facilitates the development of various lesions. A systematic review [21] identified a higher incidence of oral lesions in patients with Sjogren’s syndrome compared to patients without, the most common being angular cheilitis, atrophic glossitis, Candida infections, recurrent or chronic oral ulcerations, and tongue grooves or fissurations. BHT in the presence of Sjogren’s syndrome was previously reported in a series of 8/49 patients with Sjogren’s syndrome who underwent functional evaluation of saliva flow rate, with no other clinical information regarding their tongue lesions [22]. Therefore, the present study represents the first clinical case report of BHT in a patient with Sjogren’s syndrome. The chronic functional alterations caused by Sjogren’s syndrome comprise an underlying situation that is difficult to reverse, thus justifying the difficulty of achieving complete resolution in our patient. Of note, the complexity and difficulty of eradicating BHT in such cases should be properly communicated to the patient in order to achieve optimal management and cooperation.

It is interesting that among the most frequently reported exposure in the literature was recent or concomitant antibiotic use. Discontinuation of antibiotics led to improvement or resolution of BHT in several of these cases. This lends support to the pathophysiologic associations between antibiotic use and disruption of the oral normal flora and its protective mechanisms [5]. Of interest, besides b-lactams and linezolid, we also identified exposure to trimethoprim/sulphamethoxazole, fluoroquinolones, and macrolides in patients with BHT. Most patients with exposure to trimethoprim/sulphamethoxazole come from one case series [12] of BHT in patients with hematologic malignancies, who underwent transplantation and were also receiving chemotherapy. Therefore, trimethoprim/sulphamethoxazole exposure might have had a minimal effect on the development of the condition in comparison to the other factors reported. On the other hand, fluoroquinolones are broad-spectrum antibiotics with a wide ecological effect on the human bacterial normal flora [23,24], disrupting local microbiota and its protective functions. Macrolides have a dual effect, comprising both antimicrobial effects and non-antimicrobial effects on the immune response and cellular function [25]. The latter effects, including changes in epithelial cell apoptosis and autophagy, carry the potential to further induce epithelial disruption and other local alterations.

Despite isolating streptococcus in a throat swab culture in our patient, she did not improve with antifungals or antibiotics. Therefore, it is safe to assume that an infectious cause was not implicated in our case. In a few studies, culture results were reported for samples taken from the tongue, throat, or sputum. Among them, most samples were either negative or yielded normal oral flora. Only a few studies reported Candida species and Streptococcus species. It is, however, noteworthy that in the majority of confirmed Candida infections [26,27,28,29,30,31,32], BHT resolved with antifungals. Although the number of these cases is small, this supports the notion that in patients with BHT, oral samples should be taken to rule out fungal or bacterial infection.

There are many different ways through which drugs can contribute to the development of BHT. Several drugs, such as antimalarials, oral contraceptives, cyclophosphamide, amiodarone, bismuth-containing antacids, and phenothiazines, have been implicated in causing mucosal discoloration through deposition of metabolites, melanocyte stimulation, or deposition of erythrocyte degradation products [33,34]. The anticholinergic or sympathomimetic effects of various drug classes [35], such as antidepressants, antipsychotics, beta-blockers, antihistamines, and H2-receptor antagonists, can exacerbate mouth dryness, whereas drug interactions in patients with polypharmacy may enhance their action on saliva production [36]. Xerostomia can also be caused by the direct effect of cytotoxic drugs, such as those used in chemotherapy, on the salivary glands [33]. Drug-related taste disorders may be the result of xerostomia or various effects of the drugs or their metabolites. Such effects might be on the composition of saliva, on the taste buds, on the chemosensory signals, or by affecting the sense of smell. Taste disorders can be classified as a decrease in taste acuity (hypogeusia), a distorted sense of taste (dysgeusia), or a loss of the sense (ageusia) [35]. Typical examples of medications that affect the sense of taste include antibiotics (b-lactams, macrolides, metronidazole), ACE inhibitors, metformin, antiretroviral agents, and retinoids [33,35].

The majority of reported cases were successfully managed with removal of potential contributors when possible (e.g., discontinuation of medications) and local hygiene measures (e.g., tongue brushing, various topical solutions). Regarding outcomes, most studies reported resolution or improvement [8,9,10,11,13,14,15]. In general, elimination of possible contributors (e.g., medication) combined with oral hygiene led to resolution of the condition and symptoms.

4. Conclusions

In conclusion, we present a case report of black hairy tongue in an elderly woman with multiple comorbidities and exposures. It is our belief that oral epithelial alterations due to Sjogren’s syndrome, in combination with exposure to foods and beverages, are the most likely contributors to her tongue lesions. Current literature also supports that various different factors may contribute to the development of BHT, the most common being antibiotics, solid organ and hematologic malignancies, and immunosuppressives. Discontinuation of implicated medications, if possible, along with measures for topical care, constitutes the most effective way to achieve resolution.