Endocrine Abstracts

Introduction: Antithyroid drugs are the firstline medical treatment for hyperthyroidism in addition to symptomatic treatment (rest, beta-blockers). The most widely used in Tunisia is Thiamazole. They are generally well tolerated, but side effects have been reported. The most serious ones are agranulocytosis and liver damage. Allergic skin reactions (pruritus, urticaria) are the most common. We herein report a case of a lichenoid dermatitis bullous toxidermia induced by Thiamazole.

Case report: A 35-year-old female patient was referred to the endocrinology department of Rabta Hospital for the management of a hyperthyroidism. She presented with tachycardia, hand tremor and a weight loss, with TSH= 0.05 mUI/l and FT4 at 3 times the normal range, confirming the diagnosis of hyperthyroidism. Graves disease diagnosis was established based on the positivity of TSH receptor antibodies. Management of our patient relied on beta-blockers and Thiamazole 1 mg/day for 3 months, followed by a dose reduction to 1 mg/day with FT4 level of 21.1 pmol/l (n= 8.9 - 21.6) and TSH level of 0.11 mUI/l. After 5 months of treatment, the patient developed diffuse pruritic erythematous-papular lesions. Other drug intake was ruled out during the interview. A skin biopsy was inconclusive, showing histological features consistent with either bullous toxiderma or bullous pemphigoid. Direct immunofluorescence was performed, revealing a lichenoid dermatosis with IgM vasculitis, and a dermo-epidermal detachment supporting the diagnosis of bullous toxiderma. The decision was made to discontinue Thiamazole and initiate radioactive iodine therapy. The patient's condition improved with a reduction in lesions and disappearance of pruritus, confirming the association with Thiamazole.

Conclusion: This case illustrates the importance of meticulous clinico-biological monitoring after administration of Thiamazole, even several months after the start of treatment, as toxidermia is a potentially serious adverse drug reaction especially when associated with fever, polyadenopathy and multivisceral involvement (DRESS Syndrome), which can be life-threatening. In such rare cases, it is necessary to discontinue the ATS and switch to radical treatment.