Postpolio syndrome (PPS) is a neurologic disorder characterized by new and progressive muscular weakness, pain, and fatigue many years after the acute paralytic polio. Halstead introduced the term "post-polio syndrome" in 1986, and he published revised criteria for diagnosing PPS in 1991, in which new muscle weakness was introduced as an obligatory criterion. 
Consensus criteria for the diagnosis of PPS were published by March of Dimes and validated by a team of international experts.  The criteria are as follows:
Prior paralytic poliomyelitis with evidence of motor neuron loss, as confirmed by history of the acute paralytic illness, signs of residual weakness and atrophy of muscles on neurologic examination, and signs of denervation electromyography (EMG)
A period of partial or complete functional recovery after acute paralytic poliomyelitis, followed by an interval (usually 15 y or more) of stable neurologic function
Gradual or sudden onset of progressive and persistent new muscle weakness or abnormal muscle fatigability (decreased endurance), with or without generalized fatigue, muscle atrophy, or muscle or joint pain; sudden onset may follow a period of inactivity, or trauma or surgery; less commonly, symptoms attributed to PPS include new problems with breathing or swallowing.
Symptoms persist for at least a year
Exclusion of other neurologic, medical, and orthopedic problems as causes of symptoms
One possible cause of postpolio syndrome (PPS) is decompensation of a chronic denervation and reinnervation process to the extent that the remaining healthy motor neurons can no longer maintain new sprouts; thus, denervation exceeds reinnervation. 
A second possible mechanism for PPS is motor neuronal loss due to reactivation of a persistent latent virus. In addition to muscle atrophy and denervation, foci of perivascular and interstitial inflammatory cells have been found on 50% of biopsies of patients with PPS. Activated T cells and immunoglobulin M and immunoglobulin G antibodies specific for gangliosides also have been found.
Another possibility is an infection of the polio survivor's motor neurons by an enterovirus that is different from the one responsible for the patient's polio. Others sources hypothesize that PPS is merely the loss of strength due to the usual stresses of aging and weight gain. In patients with PPS, these processes occur in muscles that already are weak, so the consequences are more noticeable compared with those of patients who have not had polio. 
The incidence of postpolio syndrome (PPS) in previous acute polio patients ranges from approximately 22-68%. The prevalence of the PPS was estimated at 28.5% of all paralytic polio cases.  The current prevalence is approximately 1.6 million cases. Suggestions have been made that 100% of polio survivors, if tracked for a long period, can develop some symptoms of PPS. The risk of PPS was significantly higher among patients who sustained substantial permanent impairment after polio and among females. The incidence did not vary with age at acute onset, acute severity, or level of physical activity after recovery.
In a Brazilian tertiary care center, study the frequency of PPS was 77.2% of the studied population. Among them, 62.8% were women and 37.2% were men.  Prevalence rates were reported to be 31% and 41% in Italian population in 2 different studies. [7, 8] Again, it was more common in women.
PPS is more common in women.
The strongest determinant of PPS onset was the length of the interval following the acute illness, with incidence peaking at 30-34 years after acute polio.
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