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Editor,—Dapsone (diaminophenyl sulphone) has been in use for many years for the treatment of ocular cicatricial pemphigoid (OCP) as an anti-inflammatory agent. It was found to be the most effective initial agent for active or acute OCP and a safer treatment in the elderly than steroids and immunosuppressants.12 We report a previously unreported side effect of dapsone consisting of a taste disturbance and tingling sensation in the mouth and lips. This continued in the patient for about a year after commencing dapsone for acute pemphigoid and resolved following cessation of the medication.
A 70-year-old man presented to the eye casualty department with a 1 week history of sticky, red, and irritable eyes. He had no previous eye problems. His medical history included angina and myocardial infarction in 1984 and two cerebrovascular accidents (1986, 1987) with full recovery. He was taking frusemide 40 mg daily, isosorbide mononitrate 10 mg four times daily, Slow K 400 mg three times daily, aspirin 300 mg daily, and ranitidine150 mg daily. On examination, conjunctival inflammation and ulceration, symblepharons, mouth ulcers, and cutaneous blisters on the hands and face were noted. A diagnosis of acute bullous and mucous membrane pemphigoid was suspected and confirmed following dermatological consultation and skin biopsy. The patient was commenced on 80 mg daily of oral prednisolone with rapid resolution of the acute lesions. Dapsone was introduced 1 month later in a dose of 50 mg daily. The dosage of prednisolone was tapered gradually and dapsone was increased to 100 mg daily. Six weeks later the patient complained of a sickening sweet taste. The pemphigoid was completely quiet so dapsone was reduced to 50 mg daily. One year after commencing dapsone he was still in remission but complaining bitterly that everything tasted sweet with a bad taste in the mouth when getting up in morning and tingling of the face and lips. Dapsone was stopped and when he was reviewed 1 month later, all symptoms of altered taste sensation had disappeared. His eyes remained quiet using only Viscotears drops.
The main pathophysiological mechanism in pemphigoid is thought to be the formation of antibasement membrane antibodies which lead to subepithelial blistering, granulation tissue, and inflammatory infiltrate formation in the substantia propria. The infiltrates consist mainly of polymorphonuclear leucocytes (PMN) in the acute phase and also lymphocytes and plasma cells. Healing occurs by progressive fibrosis and shrinkage.34 The exact mode of action of dapsone in OCP is unknown but it appears to inhibit the migration of PMN by inhibiting lysosomal enzyme activity, interfering with the leucocyte cytotoxic system or preventing the cells from responding to chemotactic stimuli.5 A dose of 100 mg daily is usually required to control the disease in the acute phase while in the chronic phase a smaller maintenance dose of 50 mg daily or every alternate day is sufficient.5 The drug is recirculated in the liver and excreted in saliva. Side effects include haemolysis, neutropenia, agranulocytosis,6 methaemoglobinaemia, peripheral neuropathies, tremors, headaches, insomnia, anorexia, nausea and vomiting, ulcerative stomatitis, allergic dermatitis (Stevens–Johnson syndrome), depression, confusion, fatigue, raised erythrocyte sedimentation rate, pyrexia, rigors, hepatitis, and hypoalbuminaemia.7 To our knowledge, altered taste sensation (sweet taste) is not a known side effect of dapsone. No other cases have been reported to the Committee on Safety of Medicines over a period of more than 30 years (Committee on Safety of Medicines, personal communication).