Black hairy tongue with olanzapine: A rare case report.

Sir,

A 45-year-old male patient presented with a complaint of black coating on the surface of his tongue. He was being treated with tablet olanzapine 20 mg daily. The patient was not taking any other medication. He noticed coating and black discoloration on the tongue after 16 days of therapy.

Examination of the oral cavity revealed black hair-like projections on the middle and posterior one-thirds of the dorsum of the tongue. The tip and lateral sides of the tongue were normal. Buccal mucosa and teeth were normal. There were no plaques in the oral cavity.

General and neurological examinations of the patient revealed no abnormality. He was nonalcoholic and nonsmoker, and there was no history either of excessive coffee/tea intake or drug abuse. He was not suffering from any other disease except schizophrenia. There was no history of any other drug intake except olanzapine. His complete blood count, biochemical, and serological tests were normal. Scrape cytology of tongue lesion with May–Grunwald–Giemsa stain revealed abundant cellularity consisting of normal squamous cells and some elongated hair-like structures. Papanicolaou stain ruled out malignancy, and periodic acid–Schiff stain did not reveal fungal bodies. Swab from tongue patch was sterile. KOH mount from tongue scrapings did not reveal fungal elements. Fungal culture was negative. Biopsy of the lesion could not be done as the patient did not give consent for it.

Diagnosis of black hairy tongue (BHT) was made. Olanzapine was discontinued. Follow-up was done every week for 1 month. Black coating on the tongue decreased at the first follow-up (1st week). It disappeared completely at the second follow-up (2nd week) and remained so at the third and fourth follow-ups.

On Naranjo adverse drug reaction (ADR) probability scale, the score was five, which revealed a probable ADR. The ADR has been reported to the Pharmacovigilance Programme of India, with worldwide unique number IN IPC 201646573.

The exact mechanism of BHT induced by olanzapine is not known. It has been suggested that anticholinergic property of olanzapine has potential to induce BHT.[12]

To the best of our knowledge, there are only two published reports of BHT related to olanzapine. In one case, it was prescribed in combination with lithium[3] and in other with fluoxetine.[4]

We report this case to highlight the occurrence of BHT as a rare ADR of olanzapine and to sensitize clinicians about it.

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Conflicts of interest

There are no conflicts of interest.