Distal Spinal Muscular Atrophy

Distal spinal muscular atrophy is an increasingly rec­ognized group of rare diseases with varied genetic eti­ologies. More than 20 distinct genetic subtypes have been identified. The patients may be clinically misdi­agnosed as having CMT due to the distal weakness of the foot and hand intrinsics. Some subtypes of distal SMA have predominant upper extremity involvement. Other variants of distal SMA may present initially with distal lower extremity weakness. Sensory function is always normal clinically and electrodiagnostically. The course is usually slowly progressive, although some patients may experience a prolonged period of stability. Other associated features in some subtypes include vocal cord paralysis and diaphragm weakness. Some subtypes have associated pyramidal signs.