Asymptomatic Transient Lingual Hyperpigmentation

The Diagnosis: Pseudo-Black Hairy Tongue

Pseudo-black hairy tongue is a benign and painless disorder characterized by transient hyperpigmentation of the tongue with a substance that can be easily scraped off. In this case, the patient's lingual discoloration was secondary to the ingestion of bismuth salicylate. The phenomenon is thought to occur due to a reaction between bismuth and sulfur-containing compounds in the saliva, resulting in the characteristic black substance on the surface of the tongue that nestles between the lingual papillae.¹ An associated feature may include black stools. Other etiologic factors involved in pseudo-black hairy tongue include food coloring, tobacco, and other drugs such antibiotics and antidepressants.²  

The differential diagnosis of lingual hyperpigmentation includes lingua villosa nigra (also known as black hairy tongue), pigmented fungiform papillae of the tongue, acanthosis nigricans, and oral hairy leukoplakia. Lingua villosa nigra is a similar condition in which individuals present with a black tongue; however, the tongue also appears hairy. The tongue may appear as other colors such as brown, yellow, or green. Patients additionally may have symptoms of burning, dysgeusia, halitosis, or gagging. Poor oral hygiene, xerostomia, use of tobacco or alcohol, and different medications including antibiotics and antipsychotic medications increase the risk for developing lingua villosa nigra.^2,3 This condition is distinguished from pseudo-black hairy tongue by proliferation and elongation of the filiform papillae.³ Pigmented fungiform papillae of the tongue is a normal variant of tongue morphology, is more common in individuals with darker skin types, and primarily affects the lateral aspect and apex of the tongue.⁴ Acanthosis nigricans can appear in the oral cavity as multiple pigmented papillary lesions on the dorsal and lateral regions of the tongue and frequently involves the lips; this condition may be associated with metabolic disorders or underlying malignancy.^2,3 Oral hairy leukoplakia is caused by Epstein-Barr virus infection and typically presents as white plaques on the dorsal and ventral surfaces of the tongue; this condition largely is found in immunocompromised patients.⁵

In our patient there was an acute onset of tongue discoloration associated with ingestion of bismuth salicylate, no hypertrophy or lengthening of the lingual papillae, and no involvement of the patient's lips, which was consistent with the diagnosis of pseudo-black hairy tongue. Pseudo-black hairy tongue is transient and treated by discontinuation of offending agents and proper hygiene practices.