Distal vacuolar myopathy in 13 post-renal-transplant cystinosis patients, ages 17 to 27 years, and studied at multiple centers, is reported from the National Institute of Child Health and Human Development, Bethesda, MD. Among 54 untreated patients with cystinosis, 13 (24%) developed hand weakness and wasting, sometimes accompanied by facial weakness and dysphagia, and becoming progressively more generalized. Tendon reflexes were preserved, and sensory testing and nerve conduction velocities were normal. EMG of affected distal muscles showed reduced amplitude and brief duration voluntary motor unit potentials. Muscle biopsy revealed fiber size variability, acid phosphatase-positive vacuoles, and absent fiber grouping or inflammation. Muscle cystine content of clinically affected muscles was markedly elevated. The cause of the distal myopathy was unclear. Systemic complications of nephropathic cystinosis or its treatment were excluded. 
COMMENT. Distal myopathy is a relatively common late complication of nephropathic cystinosis. Cysteamine therapy may prove effective.