The antimalarials induce dysfunction of the autophagic-lysosome system resulting in pathologic autophagic vacuole formation. We present a patient where the glycogen accumulation secondary to drug induced lysosomal dysfunction was so severe that a glycogen storage disorder was initially suspected. A 74 year old woman with a past history of cutaneous lupus presented with dysphagia, reduced mobility and recurrent falls. She had been treated with hydroxychloroquine 400mg daily together with prednisolone 5mg on alternate days and rosuvastatin 5mg daily. There was no family history of neuromuscular disease. General examination showed a cachectic elderly woman without any skin rash. Neurological examination demonstrated proximal muscle weakness, quadriceps wasting, lower extremity areflexia and reduced vibration sense. Routine blood tests were normal including creatinine kinase 105 U/L. Electrophysiological examination revealed proximal myopathic and distal neuropathic patterns suggestive of a neuromyopathy. A muscle biopsy revealed severe vacuolar myopathy with florid glycogen excess leading to initial interpretation of glycogen storage disease. Electron microscopy showed pathognomonic curvilinear bodies and disruption of muscle fibres by vacuoles containing autophagic debris including myeloid bodies. A diagnosis of toxic myopathy with secondary glycogen accumulation due to acquired lysosomal damage from hydroxychloroquine was made. Statins and prednisolone are potential myotoxic agents and may have contributed to her myopathy although the type 2B fibre atrophy was not present.
Conclusion: An unusual case of hydroxychloroquine induced vacuolar myopathy mimicking a glycogen storage disorder is presented. Muscle biopsy is the definitive diagnostic test in suspected hydroxychloroquine myopathy. Electron microscopy is essential to demonstrate the diagnostic curvilinear bodies.