[Isoniazid-induced myopathy]

Drug-induced muscle disorders are now well known and vary from a simple isolated increase in muscle enzymes to severe drug-induced myopathy. The list of drugs inducing myopathy is very long and continues to grow. The onset of muscle disorders under isoniazid often falls within a drug-induced neuropathy or a drug-induced lupus. However, the occurrence of isolated isoniazid-induced drug myopathy without neuropathy is an extremely rare condition especially with non-toxic doses. The authors report the case of a 28-year-old man, without a previous medical history, hospitalized for pulmonary tuberculosis. After initiating tuberculosis treatment for five days, he presented muscle pain, fasciculation and weakness initially involving the lower left limb that quickly propagated to all four limbs. The physical examination noted a left ankle flush, a swollen left calf and fasciculation of both calves while the neurological examination was normal. The CPK was normal. Electromyography confirmed the myopathy without neuropathic findings. Isoniazid withdrawal was marked by the rapid disappearance of the symptoms. The reintroduction of a half-dose of isoniazid only induced a few transitional muscular fasciculations. The onset of the symptoms under tuberculosis treatment, the absence of later muscle disorders, the absence of any other cause of myopathy and the total disappearance of the symptoms after isoniazid withdrawal confirmed the diagnosis of isoniazid-induced myopathy.