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Muscle dysfunction related to clozapine treatment is largely unrecognized. We evaluated weekly creatine kinase(CK)levels in 37 consecutive clozapine- treated outpatients with chronic psychotic disorders.Those with CK elevations underwent clinical neurologic evaluation,electromyography(EMG), and nerve conduction studies.Patients with probable myopathy had a quadriceps muscle biopsy.Twenty control patients had a single CK level determination.Twenty-nine of 37 clozapine-treated patients had CK elevations.Three patients had extreme CK elevations(>20,000 IU/L),without myoglobinuria.Mean CK levels were significantly greater in clozapine patients(194 IU/L)than in control patients(142.3,P=0.033).Of 18 clozapine- treated patients evaluated clinically,6 had mild proximal weakness.EMG in 13 patient was myopathic in 5,normal in 5,and neurogenic in 3.Muscle biopsy in 5 patients showed rare regenerating myofibers and mild acute denervation(1),mild type II fiber atrophy(1),minimal acute denervation(1), and normal muscle(2).In conclusion,clozapine therapy may be associated with CK elevations and,rarely,mild myopathy. |
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