Clinical Signs of Poliomyelitis
Most poliovirus infections are asymptomatic, but when clinical disease occurs, it presents with a characteristic biphasic pattern: initial nonspecific febrile illness followed by potential progression to aseptic meningitis or paralytic disease, with the hallmark finding being asymmetric flaccid paralysis with absent deep tendon reflexes. 1
Initial Phase (Nonspecific Febrile Illness)
The first phase presents with nonspecific symptoms that are indistinguishable from many viral illnesses 1:
- Fever is the predominant early sign 1
- Sore throat, headache, and upper body stiffness may occur 2
- Respiratory illness symptoms or gastroenteritis manifestations can be present 3
- This phase occurs during the 7-21 day incubation period (range 4-30 days) 1
Paralytic Poliomyelitis (0.1-1% of infections)
When paralysis develops, it progresses rapidly with distinctive motor neuron characteristics 1:
Temporal Pattern
- Rapid progression to maximum paralysis within 2-4 days 1
- Fever and muscle pain accompany the paralytic phase 1
Neurologic Findings
- Asymmetric spinal paralysis that is characteristically more severe proximally than distally 1
- Absent or diminished deep tendon reflexes - a critical distinguishing feature from upper motor neuron lesions 1
- Muscle atrophy and weakness affecting specific muscle groups 2, 4
- Pure motor involvement without sensory deficits, as polio is an anterior horn cell disorder 5
Bulbar Involvement
- Bulbar paralysis can compromise respiration and swallowing when the medulla oblongata is affected 1
- Dysfunction of swallowing mechanisms with potential respiratory and circulatory distress 2
Clinical Categories
Poliomyelitis manifests in four distinct clinical forms 3:
- Inapparent infection - asymptomatic (majority of cases)
- Abortive poliomyelitis - mild illness without neurologic involvement
- Nonparalytic poliomyelitis - aseptic meningitis without paralysis
- Paralytic poliomyelitis - the severe form with motor neuron destruction
Diagnostic Pitfalls
- Polio can be misdiagnosed as Guillain-Barré syndrome, polyneuritis, or transverse myelitis 1
- The key distinguishing feature is that polio causes anterior horn cell destruction (central nervous system disorder with peripheral manifestations), not peripheral nerve damage 5
- EMG findings show denervation with fibrillation potentials, positive sharp waves, and fasciculations reflecting motor neuron loss 5
Prognosis and Recovery
- Paralytic polio is fatal in 2-10% of cases 1
- Many patients recover at least some muscle function after the acute episode through terminal sprouting and reinnervation 1, 6
- Prognosis for recovery can be established within 6 months after onset of paralytic manifestations 1
- The period of communicability continues for 4-6 weeks after infection 1
Post-Polio Syndrome (Late Manifestation)
- After 30-40 years, 25-40% of paralytic polio survivors develop post-polio syndrome with new muscle weakness, pain, and exacerbation of existing weakness 1, 5
- Risk factors include longer time since acute infection, permanent residual impairment, and female gender 1
- Polio survivors fall up to four times more often than age-matched peers due to impaired balance control and slow gait 4