Centronuclear Myopathy Mimicking Distal Myopathy otherwise normal. There was marked atrophy of both calf muscles (Fig. 1). Deep tendon reflexes were hypoactive on both upper and lower extremities without pathological reflex- es. She had a mild waddling gait, and toe gait was more im- paired than heel gait. There was no myotonia, fasciculation, winged scapula, or pseudohypertrophy. Examinations of cra- nial nerves and sensations revealed no abnormality, and her cognitive function was normal. Her serum creatine kinase (CK) was slightly elevated to 304 IU/L (normal, <270 IU/L), but other routine laboratory tests, Fig. 1. Photograph of the patient. Note the marked atrophy in the posterior compartment of the lower legs. 1099 including thyroid function, were all within normal limits. Electrocardiogram, pulmonary function test, and nerve con- duction studies were unremarkable. Needle electromyogra- phy showed low-amplitude, short-duration, polyphasic motor unit potentials along with fibrillations and positive sharp waves in the left vastus lateralis, tibialis anterior, and gastrocnemius muscles. There was no myotonic discharge. The magnetic res- onance image of the lower extremities revealed predominant atrophy and fatty changes of bilateral gastrocnemius and soleus muscles (Fig. 2). A muscle biopsy from the right tibialis ante- rior showed centrally located nuclei in the vast majority of muscle fibers with marked fiber size variations. A moderate degree of endomysial fibrosis and fatty changes were also noted. NADH tetrazolium reductase staining showed type 1 fiber predominance (more than 95%) and hypotrophy, while some fibers revealed radially arranged sarcoplasmic strands (Fig. 3). Electron microscopy also showed marked fiber size variations and centrally located nuclei in myofibers frequently. All of these pathologic features suggested centronuclear myopathy. Case 2 The 18-yr-old daughter of case 1 complained of difficulty in walking and during physical exercise from the age of 15. The neurological examinations showed a weakness in the ankle dorsiflexors and plantar flexors (MRC grade 5-), im- paired toe and heel gaits, mild atrophy of both calf muscles, and hypoactive tendon reflexes. Examinations of cranial nerves, sensations, and cognitive function revealed no abnormality. Nerve conduction studies were unremarkable. Needle elec- tromyography revealed low-amplitude, short-duration, poly- phasic motor unit potentials along with fibrillations and pos- A B Fig. 2. MR images of the lower extremities. Note the predominant atrophic and fatty changes of bilateral gastrocnemius and soleus mus- cles (arrowheads) on T2-weight axial (A) and coronal (B) images.