A PREVIOUSLY healthy female infant developed vomiting, lethargy, poor oral intake, gray coloring, and decreased lower extremity movement at age 8 weeks. Respiratory acidosis prompted intubation. An electromyogram (EMG) showed disorganized muscle fibrillations consistent with inflammatory myopathy. Trials of intravenous immunoglobulin and methotrexate proved ineffective. Muscle weakness and stiffness progressed for the next 2 years (Figure 1), and creatine kinase levels were increased. At age 2 years, she lost all motion of the knees and elbows and developed spontaneous dislocation of the hips with preserved mobility of ankles and wrists. Impaired swallowing and decreased diaphragmatic and thoracic cage compliance resulted in a need for mechanical ventilation. The EMG of the right deltoid, vastus medialis, and tibialis anterior muscles at rest showed spontaneous fibrillations and sharp waves superimposed on normal-appearing motor unit action potentials. Nerve conduction studies were normal. Abdominal wall muscle biopsy from age 4 months showed marked fiber size variation and endomysial fibrosis; a deltoid muscle biopsy at age 9 months showed patchy sarcoplasmic granular basophilia with small eosinophilic inclusions (Figure 2). Severe fiber hypertrophy and atrophy with frequently necrotic and granular fibers characterized biopsy findings. Marked interstitial inflammation with myofiber phagocytosis and interstitial fibrosis complete the dystrophic picture (Figure 3). Viral studies were negative. Electron microscopic studies showed extensive, patchy Z-band transformation into granular, punctate densities interspersed with thin filaments. Subsarcolemmal autophagic vacuoles contained whorled membranes resembling myelin. The nuclei showed finely granular chromatin with no evidence of viral particles (Figure 4). The abnormal spontaneous muscle activity persisted during general anesthesia and during a curare-induced right common peroneal nerve block. By age 4 years, she lost all volitional motion except oral, ocular, and distal finger movements. At age 6 years (Figure 5), she remained at or above cognitive peer-appropriate levels with stable ventilatory requirements.