To understand the mechanism of
post-poliomyelitis muscular atrophy (PPMA) and the
post-polio syndrome (PPS) in general, we performed the following studies: (1) histopathology in spinal cord sections from patients who died 9 days to 44 years after acute paralytic
poliomyelitis; (2)
enzyme histochemistry, immunocytochemistry (for lymphocyte subsets, MHC
antigens and N-CAM) and polymerase chain reaction (PCR) for poliovirus
RNA in the muscle biopsies from symptomatic or asymptomatic muscles of post-
polio patients; (3) determination of lymphocyte subsets and circulating
IgG or
IgM antibodies against GM1 and poliovirus; (4) virological studies in the spinal fluid for
oligoclonal bands and search for poliovirus genome with PCR; (5) electrophysiological studies including single fiber EMG, fiber density and macro-EMG; and (6) [31P] exercise MRS spectroscopy on previously affected muscles to search for a metabolic correlate of
fatigue. These studies concluded that in PPS a continuing dysfunction is present in the spinal cord motor neurons, resulting in ongoing
muscle denervation and reinnervation first evident at the axonal branch points. Symptoms are related to attrition of the oversprouting motor neurons which after a period of time cannot support all their axonal sprouts, resulting in failure of re-reinnervation. In some patients with PPS there is also an ongoing immune activation and presence of defective viral particles in the spinal fluid. However, their role in the pathogenesis of PPS is presently unknown.