Reversible myotonic myopathy induced by colchicine: A rare mimic of myotonic dystrophy

Abstract

Colchicine is widely used in the treatment of familial Mediterranean fever (FMF) and other inflammatory disorders and is generally well tolerated. However, neuromuscular toxicity may rarely occur. Although colchicine-induced myopathy has been increasingly recognized, the coexistence of clinical myotonia with electrophysiologically documented myotonic discharges remains exceptionally uncommon. We report a 45-year-old woman with FMF who developed diffuse myalgia and progressive gait disturbance over five days following an increase in colchicine dosage to 3 mg/day. Neurological examination revealed proximal muscle weakness and percussion myotonia. Laboratory studies showed elevated creatine kinase and hepatic transaminase levels, with preserved renal function. Muscle magnetic resonance imaging was normal, myositis-specific antibodies were negative, and nerve conduction studies were unremarkable. Needle electromyography demonstrated myogenic motor unit potentials with prominent myotonic discharges, predominantly in proximal lower-limb muscles. Colchicine was promptly discontinued, and intravenous hydration was initiated. Within one week, liver enzyme levels normalized, clinical myotonia resolved, and repeat electromyography showed complete disappearance of myotonic discharges, although mild myopathic features persisted. The absence of multisystem involvement, family history, and the rapid clinical and electrophysiological recovery after drug withdrawal strongly argued against a hereditary myotonic disorder and supported a diagnosis of colchicine-induced myopathy with transient myotonia. This case highlights a rare but reversible manifestation of colchicine-related neuromuscular toxicity and emphasizes the importance of considering a pharmacological etiology in patients presenting with acute or subacute proximal weakness and myotonia. Early recognition and prompt withdrawal of colchicine are essential, as clinical and electrophysiological recovery is typically complete.