Rough Brown Patch on the Center of the Tongue of an Old Man, Which Does Not Scrape Off

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HISTORY

A 78-year-old man examined on rehabilitation unit, where he has been receiving intensive physical therapy after uneventful total knee arthroplasty. Has noticed blackish discoloration of his tongue. No known alcoholism, vitamin deficiency, recent antibiotics other than usual 2 perioperative prophylactic doses of cefazolin. No use of psychoactive medicines. Does not smoke nor chew tobacco.

PHYSICAL EXAMINATION

Generally healthy-appearing man who looks stated age, though facial stubble gives false impression of self-care deficit. Tongue as illustrated; material on the surface did not scrape off with a tongue blade. No other lesions in or about the mouth. No cervical lymphadenopathy. Skin, heart, lungs, abdomen, neurologic and mental status unremarkable.

WHAT'S YOUR DIAGNOSIS?

(answer on next page)

WHAT'S YOUR DIAGNOSIS?
ANSWER: BLACK HAIRY TONGUE

Across an area at least 4 cm across that covers its center, the dorsum of the tongue is coated with brownumber material that is irregular at its margins, and “cobblestoned” to form a rough, irregular surface throughout. The coating matter gives an impression of standing up in little bristles, particularly when the most posterior part midline is scrutinized closely (Figure). Based on locale and morphology, this constitutes black hairy tongue, though it is not black and looks more velvety than hairy.

Black hairy tongue, a painless and innocuous condition that is much misunderstood, has been reported in association with numerous conditions and medicines.^1-17 It is not a marker of any systemic process, nor an indicator of significant intra-oral disease, though it is increased in persons who have (non-oral) cancer,¹ and in asymptomatic tobacco users.² The sign is not useful as a surface marker of internal malignancy, since it is found in so many normal hosts that it lacks meaningful specificity.

INCOMPLETE INFORMATION ON PATHOGENESIS
Limited biopsy work shows that the histopathologic basis of the sign is elongation of one set of taste buds, the filiform papillae, by hyperkeratosis.¹ These particular taste buds lie anterior to the large rounded circumvallate papillae that form a V as far back as a (non-dentist) clinician can see on examination. None of them are found forward and laterally as are the fungiform (mushroom-shaped) papillae that can make little knobs at and near the tip of the tongue. The name filiform tells us that even in the normal state, the buds in question resemble threads in being narrow and long. Thus the “hairy” attribute of black hairy tongue merely exaggerates a baseline characteristic. A substantial subset of cases are explained by loss of the mechanisms that help keep the filiform papillae from overgrowing in the normal state, namely ordinary abrasion of tongue against food bolus, palate, and teeth. Thus we can safely predict that this lesion is more common in the edentulous (if they don't use dentures) and in those who eat only pureed food.

Over time, the color evolves: the abnormal papillae can start out white, tan, or pinkish. They then retain dark bacteria both living and dead, fungi,^3,4 food particles, bits of tobacco, fragments of tea or coffee, or medication residues.^4,5 The final color can range from yellow to yellow-brown, to a deeper brown as here, to ink-black.

The old inference that the “hairs” were mycelia of Aspergillus niger-hence the black color-or pseudohyphae of Candida that had overgrown because of disrupted oral flora, lacks morphologic support. The hypothesis was attractive, since black hairy tongue often follows antibiotic therapy and commonly recedes after such therapy is completed, but the scale of the “hairs” exceeds the individual fungal forms mentioned by orders of magnitude.

PATHOPHYSIOLOGY HASH
Endless papers describe the features of black hairy tongue and the drugs or comorbid diseases of those who display it. Our reference list offers only a small sample of this literature. Insights about mechanism are sparse-with gratifying exceptions such as a report of unilateral black hairy tongue in trigeminal neuralgia, wherein the patient avoided chewing on the affected side, thus reducing the frictional turnover that occurs physiologically.⁶ One recent article asserts that we understand little more than at the time of the first modern description in 1925.⁷ Many current reports suggest confused nosologic or pathophysiologic inferences in the rush to publication, as in a case with a Nikolsky-like phenomenon that is not accounted for,¹⁰ or another in which olanzapine is implicated but the patient recovers with only modest reduction in dose.¹¹ Even useful brief reviews can forward glaring omissions, as in the lack of acknowledging the primary cutaneous (non-oral) involvement of acanthosis nigricans, and its frequent non-cancerous association with endocrinopathies.⁵

To my knowledge, no satisfactory explanation has emerged as to the enhanced prevalence during and just after antibiotic therapy; clearly some instances of candidal glossitis have been misdiagnosed as black hairy tongue, and the predilection to thrush with antibiotics is easy to understand.

Given that staining by tobacco is usually granted a role in this condition, it is not clear why black hairy tongue is seen in at least as many ex-smokers as current smokers. Likewise unknown is a convincing mechanism by which oxidant mouthwashes lead to its appearance in some persons. Attempts to implicate a common pathway of irritative overproduction of keratin, even without dysplastic cellular proliferation, have been advanced, but convincing evidence in support is lacking.

Finally, the mouth-drying (xerostomic) effects of several drugs have been claimed to play a role. However black hairy tongue is not a consistent or prominent problem in persons who have longstanding non-pharmacogenic xerostomia, either from age or as part of keratoconjunctivitis sicca.⁸

MIMICS
Several other conditions can be confused with black hairy tongue: Just as with white patches, extrinsic staining from food or liquids always deserves consideration. If the dark material scrapes off with a tongue blade, it is foreign matter. A well-documented case showed darkening of tongue and saliva during nortriptyline therapy, without known risk factors for black hairy tongue; this coincided with use of the agent and remitted shortly after discontinuation of therapy. No “hairy” element was present, and whatever entity this might have been, it was not black hairy tongue. Curiously, serum and salivary levels of nortriptyline in that patient were similar to those of patients taking the drug who never had this complication.¹³

Pigmented fungiform papillae are seen in some dark-skinned persons, but occupy a very different locale on the tongue.^5,9

Pigmented oral mucosal spots can be seen in darkskinned persons, usually without involvement of the lingual mucosa. In persons who use tobacco, smoker's melanosis is seen on the alveolar gingival mucosa of both upper and lower jaw-also prime territory for pigment in darker-skinned persons who do not smoke- and in pipe smokers, on the cheek and the commissures of the lips. Note that the tongue is not expected to be part of any of this.

Hairy leukoplakia, chiefly in persons with advanced HIV disease, is readily distinguished by its tendency to involve not the dorsum but the lateral surface of the tongue; and by its white color.

Black infarcts of the tongue are well known in giant cell arteritis^18-23 but do not occur in the absence of symptoms. They evolve just as does ischemic coagulative necrosis in other sites, and since they result from arteritic obstruction of lingual arteries, they do not spare the distal and lateral portions, although they can be purely unilateral.

Melanoma of the tongue occurs extremely rarely, and warrants a thought if the locale differs, or if an ulcer is seen, or induration, or there is a more classic exophytic appearance.

One can also find nonselective staining of mouth linings in those few and bizarre persons who hold a bismuth preparation in the mouth for a long time before swallowing: a less familiar counterpart of the common finding of black stools with a negative test for fecal hemoglobin in persons who use bismuth subsalicylate (Pepto-Bismol). Despite the disgust that the final differential diagnosis will engender, for completeness one mentions that the tongue could be stained brown-black in a coprophage; the context would be only too obvious and nonselective from odor and demeanor.

INTERVENTIONS
Many patients only need reassurance that despite the Halloween-like caricature one might carry about a black-centered tongue, nothing ominous is at hand.

An immense variety of medications, both topical and systemic, have been tried as remedies, some of which may also cause the condition. Radiotherapy was employed in a case reported half a century ago, at which we now shudder.¹⁶

Highest success rates follow regular tongue brushing- with a soft brush, we are not torturers!-twice daily, and the cessation or reduction of tobacco, tea, caffeine, and any of the medicines on the long list associated. Of course if there is doubt about the nature of the problem, or difficulty in satisfying the patient's fears or achieving an acceptable cosmetic result, early consultation with a dentist is mandatory.

Shearing of the elongated papillae with scissors has been recommended, and if there is no fibrovascular core of the “hairs,” as the pathology suggests,¹ this should be painless, bloodless, and safe even without anesthetic. Perhaps I am overly staid, but I do not aspire to give any patient's tongue a haircut.

Schneiderman H. Black hairy tongue (lingua vellosa nigra), its differential diagnosis and its innocence. CONSULTANT. 2009;49:705-708

References:

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