Differential diagnosis of acute flaccid paralysis and its role in poliomyelitis surveillance.

Acute flaccid paralysis (AFP) is a clinical syndrome characterized by rapid onset of weakness, including (less frequently) weakness of the muscles of respiration and swallowing, progressing to maximum severity within several days to weeks. The term "flaccid" indicates the absence of spasticity or other signs of disordered central nervous system motor tracts such as hyperreflexia, clonus, or extensor plantar responses (1). When applied to voluntary muscles, "paralysis" means loss of contraction due to interruption of motor pathways from the cortex to the muscle fiber. It is preferable to use the term "paresis" for slight loss of motor strength and "paralysis" or "plegia" for severe loss of motor strength (1). The differential diagnosis of AFP varies considerably with age. No single operational clinical case definition of AFP or paralytic poliomyelitis that combines both high sensitivity and high specificity has emerged (2-4). The currently used case definition increases sensitivity in detecting the existence of AFP but tends to decrease specificity in detecting paralytic poliomyelitis.