OPDM

The mean age of onset of this progressive disease is 22 years.  Pharyngeal and distal limb muscles seem to be primarily involved.  Weakness in masseter, facial, and bulbar muscles have been observed but no muscle group seems to be spared.  Atrophy of facial muscles is common and may be pronounced.  There is considerable variability in expression, particularly in the degree of limb weakness which often appears by the fifth decade.  Swallowing difficulties can be severe.  Respiratory weakness may be evident relatively early, even while patients are still ambulatory.  Loss of ambulation most commonly occurs by the third or fourth decade after the onset of first symptoms.  Serum creatine kinase levels are mildly elevated and histologic changes show chronic myopathic changes with rimmed vacuole formation.  No changes have been found in the central or peripheral nervous system.