Post-polio Syndrome: An Overview

Poliomyelitis was a dreaded disease of devel­ oped countries, affecting tens of thousands of children and adults during each of the epidemic years up to the mid-1950s. The polio virus is a small RNA virus whose only natural host ap­ pears to be man. The vast majority of exposed persons develop either an inapparent infection or a non-specific flu-like illness (non-paralytic poliomyelitis). Secondary invasion of brain and spinal cord is associated with infection and death of motor neurons, with loss of innerva­ tion to muscle fibers, and consequent muscle weakness and atrophy. Postmortem studies show that muscle weakness in poliomyelitis is clinically apparent only when more than half of corresponding motor neurons are destroyed. Frequently, muscles can be reinnervated by healthy neighboring motor neurons by a pro­ cess of axonal sprouting. Thus, partial or com­ plete recovery of muscle bulk and strength can occur, in which subnormal numbers of motor neurons support increased (up to 8-fold) numbers of muscle fibers. It is estimated that about 250,000 people in the United States have survived paralytic poliomyelitis and are alive today.