Patients with post-polio syndrome are more likely to have subclinical involvement as compared to polio survivors without new symptoms.

Background: Post-polio syndrome (PPS) is a condition that affects polio survivors decades after recovery from an initial acute attack. It is a well-known entity that limbs thought to be nonaffected by polio survivors commonly demonstrate electromyography (EMG) evidence of prior polio. Although the diagnosis of PPS requires a remote history of acute paralytic polio, clinically unapparent damage caused by poliovirus can be associated with PPS later in life. Objective: To evaluate EMG abnormalities and late progressive symptoms in limbs thought to be nonaffected by polio survivors, in order to determine the prevalence of subclinical motor neuron involvement in those fulfilling criteria for PPS comparing to those without such symptoms. Materials and Methods: Clinical and EMG findings of 464 limbs in 116 polio survivors who had been admitted to our clinic were analyzed. Affection of the limbs by polio was classified based on the patient's self-report on remote weakness during the acute phase of poliomyelitis, muscle strength measured by manual muscle testing, and four-limb needle EMG. Results: Seventy-six of the patients (65.5%) met the criteria of PPS. Needle EMG studies revealed subclinical involvement in 122 out of 293 (42%) limbs with no history of remote weakness during the acute phase of poliomyelitis. Prevalence of subclinical involvement was found 47% in polio survivors who met the criteria of PPS compared to 33% in those without PPS ( P = 0.013). Among the limbs that had developed new weakness in PPS patients, 33.5% had subclinical involvement. Discussion and Conclusion: Subclinical involvement is common in limbs thought to be nonaffected by polio survivors, and this is especially present in those fulfilling criteria for PPS. New muscle weakness may develop in apparently nonaffected, subclinically involved muscles. Thus we believe that four-limb EMG studies should be performed in all polio survivors, especially in those with the symptoms of PPS.