Postpoliomyelitis syndrome (PPS) is a neurological disorder that occurs in individuals with a history of recovering from symptoms of paralytic poliomyelitis. After many years or decades of neurological stability (median 25 years), patients present with new progressive weakness, fatigue, and pain. The cause of this syndrome is unknown. The course of illness is typically slowly progressive and can involve dangerous respiratory compromise but is not fatal and is variable in its progression.

While exact pathophysiology is unknown, those with more severe initial paralytic symptoms as well as those with more significant recovery are more likely to have PPS. These findings are explained by the most widely accepted hypothesis by Wiechers and Hubbell. In this theory, those with more severe initial symptoms would have had more significant denervation damage to motor neurons and more denervation of muscle fibers. Recovery occurs with surviving motor neurons expanding their field of innervation up to 20 times their original number of muscle fibers innervated. These overextended motor neurons are felt to be more susceptible to natural aging changes as well as excessive metabolic stress, such as exercising to exhaustion (another risk factor for the development of PPS).

Risks of developing PPS include longer time since initial disease, increased severity of initial deficits, significant recovery and significant remnant deficits, greater activity level in years between disease and PPS (especially vigorous exercise), and older age at time of disease.

The onset of symptoms of PPS is generally insidious but can present acutely or in a stepwise fashion. The most common signs are weakness, fatigue, and pain. Fatigue is the most common symptom and occurs in a majority of patients and is usually associated with general fatigue and specific muscle groups, often worsened by increased activity. It can be associated with decreased concentration and increased daytime napping, and improved with increased sleep.

Pain is the next most common symptom and can exist in joints, bones, or muscles, generally minimal in the morning and worsening as the day continues, characterized most commonly by a dull, aching soreness.

Muscle weakness is most commonly seen in muscles originally involved in the paralysis, but it can occur in previously uninvolved muscle groups.

Other symptoms can include cold intolerance, dysphagia, dysphonia, dysarthria, and new shortness of breath, sleep apnea, or daytime sleepiness. Hypoventilation itself is rare.