Researchers at the National Neuroscience Institute, Riyadh, Saudi Arabia, report a series of 8 patients with type III spinal muscular atrophy who were referred with a diagnosis of muscular dystrophy. Developmental milestones were normal until early juvenile or teens years when they showed a slowly progressive proximal weakness involving limb-girdle muscles. A clumsy gait was associated with frequent falls and difficulty in climbing stairs. Seven patients were products of consanguineous marriage. Hypertrophy of calves in 3 patients contrasted with generalized muscle wasting. Tongue fasciculation occurred in 2 patients, deep tendon reflexes were diminished in 7, and spinal scoliosis developed in 5. Muscle biopsy had nonspecific myopathic features in 3 patients, and nerve conduction studies showed normal, mildly neurogenic or myopathic changes. Serum creatine kinase levels varied from normal to significantly elevated. The diagnosis of SMA III was confirmed by gene testing where deletions of exon 7 were detected in all patients. [1]
COMMENT. In the diagnosis of SMA type III, the presence of dystrophic features such as calf muscle hypertrophy, limb-girdle muscle weakness, elevated serum CPK, and myopathic or dystrophic muscle biopsy findings will sometimes lead to confusion with muscular dystrophy. Diagnosis is confirmed with a molecular genetic polymerase chain reaction-based test for 5q telomeric SMN1 mutation.