Methimazole-induced myositis: a case report and review of the literature

Abstract

SummaryMethimazole is an anti-thyroid drug commonly used to treat hyperthyroidism and is a relatively safe medication. Several side effects have been reported and usually develop within 3 months of therapy. Well-known adverse reactions include agranulocytosis, hepatitis, skin eruptions, and musculoskeletal complaints such as myalgia, arthralgia, and arthritis. So far, myositis secondary to carbimazole was described in the context of a lupus-like syndrome or other rare cases of anti-neutrophil cytoplasmic antibodies-associated vasculitis. Methimazole-induced myositis occurring independently of such reactions was rarely stated. We report a patient with hyperthyroidism who, early after therapy with methimazole, developed hepatitis, eosinophilia, and fever that resolved completely after stopping the medication as well as a delayed onset of biopsy-proven eosinophilic myositis and fasciitis of gluteal muscles that resolved eventually without any additional therapy. Therefore, we raise the awareness regarding a rare side effect of methimazole: myositis.Learning points Several differential diagnoses arise when managing a hyperthyroid patient with muscle complaints.Both hyperthyroidism and methimazole are associated with myositis.Methimazole-induced myositis is a rare clinical entity.Resolution of symptoms may occur after stopping methimazole.

Erratic movement disorders disclosing Graves’ disease and paralleling thyroid function but not autoantibody levels

“…Our patient exhibited myalgia, an extremely rare complication of both of the oral anti-thyroid treatments, 21,22 which vanished after stopping the treatment. The normal clinical and blood test results after disappearance of the muscle pain prevented us from hypothesizing as to the underlying mechanisms.…”

Carbimazole induced rhabdomyolysis

“…Skeletal muscle constitutes a significant proportion of our body mass and relies on thyroid hormone for optimum development, function, and regeneration ( 1 , 2 , 3 , 4 , 5 ). Thyroid dysregulation, unsurprisingly, can lead to myopathic symptoms and altered basal muscle metabolism ( 1 , 2 , 3 , 4 , 5 , 6 ).…”

“…Skeletal muscle constitutes a significant proportion of our body mass and relies on thyroid hormone for optimum development, function, and regeneration ( 1 , 2 , 3 , 4 , 5 ). Thyroid dysregulation, unsurprisingly, can lead to myopathic symptoms and altered basal muscle metabolism ( 1 , 2 , 3 , 4 , 5 , 6 ). While musculoskeletal complaints are common in thyroid disorders, skeletal muscle is also vulnerable to the circulating ATD used to combat these disorders ( 1 , 2 , 4 ).…”

Creatine Kinase Elevation during Antithyroid Treatment of a Patient with Graves’ Disease: A Case Report and Review of Literature

“…Authors speculated that the acute decrease of thyroid hormones in tissues following a state of chronic hyperthyroidism may result in relative hypothyroid states and subsequent alterations in CK concentrations as Suzuki et al mentioned before [7]. Khalil et al reported a case of MMI-induced myositis that resolved after withdrawal of the offending drug [8]. Chieh-Hua Lu described 2 cases presented with complaints of myalgia and muscle cramps, and serum CK elevation a few weeks after initiation of antithyroid treatment.…”