Pulmonary Medicine

Neuromuscular Disorders Affecting the Thorax: Poliomyelitis and Post poliomyelitis syndrome

What every physician needs to know

Twenty-five percent of cases of acute poliomyelitis are characterized by paralysis, which may be severe enough to require mechanical ventilation. Respiratory muscle function typically returns to normal, but progressive muscle weakness in the form of post-polio syndrome (PPS) may occur years later.

Post-poliomyelitis syndrome (PPS) incorporates neurologic and musculoskeletal features that occur, on average, 29 years following recovery from acute poliomyelitis. PPS develops in 20-60% of cases of prior acute poliomyelitis, with a mean age at onset of 51 years.

Classification

Not applicable.

Are you sure the patient has poliomyelitis or post-poliomyelitis syndrome? What should you expect to find?

The most common findings in acute poliomyelitis include weakness in one or more muscle groups; asymmetric reduction in muscle tone that affects proximal muscles more than distal muscles and involves the lower extremities more than the upper extremities; decreased or absent deep tendon reflexes; normal sensory examination; encephalitis in the infantile form; and dysphagia, dysarthria, and difficulty handling oral secretions (bulbar symptoms) in up to 30% of patients.

Commonly seen findings in PPS include progressive weakness, which always occurs in the muscle groups that were affected during the initial illness. The weakness is usually asymmetric, and it may be proximal or distal. Atrophy is present in 50% of patients. Fatigue is the most common symptom, occurring in 80% of patients. Associated pain is due to spinal deformities (kyphoscoliosis), degenerative joint disease, or joint instability. Another common symptom of PPS is decreased ability to ambulate.

PPS is characterized by slowly progressive respiratory failure that is typically due to muscle weakness but can also be related to central hypoventilation. The average annual decrease in forced vital capacity (FVC) is 18.6 ml/year (1.9%/year). Recurrent aspiration is common. PPS occurs earlier in those with more severe initial disease and is more likely with adolescent- or adult-onset poliomyelitis than with cases arising during infancy. The more profound the recovery from the initial bout of poliomyelitis, the greater the likelihood of development of PPS.

Beware: there are other diseases that mimic poliomyelitis and post-poliomyelitis syndrome:

Other neurologic syndromes that may be confused with poliomyelitis or PPS include ALS, Guillain-Barre syndrome, West Nile virus, other non-polio enteroviruses, diphtheria, botulism, radiculopathy, neuropathy, and myopathy.

How and/or why did the patient develop poliomyelitis or post-poliomyelitis syndrome?

The cause of PPS is unknown. Hypotheses include muscle denervation followed by aberrant re-innervation, susceptibility to aging of re-innervated motor units that were previously affected, overuse of previously damaged muscles, and immune-mediated injury to abnormal motor units.

Which individuals are at greatest risk of developing poliomyelitis or post-poliomyelitis syndrome?

Prior to the widespread use of oral polio vaccine in 1954, poliomyelitis was a common cause of neuromuscular respiratory failure. Acute poliomyelitis, now rare in the U.S., occurs predominantly in those with exposure to oral polio vaccine and in unimmunized individuals. However, the sequelae of acute poliomyelitis still affect a large number of people; most survivors have decreased muscle strength and function.

PPS is a relatively new, progressive disability that occurs decades after the initial acute illness, with an incidence of approximately 20-30%. PPS is diagnosed on clinical grounds using a number of diagnostic criteria, including a prior episode of acute poliomyelitis with residual motor neuron loss; an interval of at least 15 years from a prior episode of acute poliomyelitis, during which neurologic stability was evident; the gradual onset of new weakness and abnormal muscle fatigability for longer than one year; and exclusion of other medical conditions.

What laboratory studies should you order to help make the diagnosis, and how should you interpret the results?

Routine laboratory studies are usually normal in PPS and the CSF may be normal or show mildly increased protein or oligoclonal bands in PPS. In addition, exercise may lead to an increase in CPK in PPS.

What imaging studies will be helpful in making or excluding the diagnosis of poliomyelitis and post-poliomyelitis syndrome?

Not applicable.

What non-invasive pulmonary studies will be helpful in making or excluding the diagnosis of poliomyelitis and post-poliomyelitis syndrome?

Additional testing is usually not helpful.

What diagnostic procedures will be helpful in making or excluding the diagnosis of poliomyelitis and post-poliomyelitis syndrome?

No confirmatory tests are available to distinguish residual findings of prior acute poliomyelitis from PPS. The EMG does not clearly distinguish PPS from prior poliomyelitis, and muscle biopsy does not readily distinguish between the two.

What pathology/cytology/genetic studies will be helpful in making or excluding the diagnosis of poliomyelitis and post-poliomyelitis syndrome?

Pathologic, cytologic, and genetic testing are not helpful.

If you decide the patient has poliomyelitis or post-poliomyelitis syndrome, how should the patient be managed?

Care is largely symptomatic and supportive. Generalized fatigue is addressed through use of energy conservation techniques and an exercise program, while muscle weakness may be improved through use of non-fatiguing exercises. Modafinil is not helpful.

Management of respiratory dysfunction is important. Early noninvasive ventilation may be beneficial in reversing chronic hypoventilation and improving respiratory muscle strength and exercise capacity. Once the vital capacity drops below 1L, assisted ventilation is often necessary. Intravenous immunoglobulin (IVIG) may be beneficial although additional clinical trials are necessary to address the value of IVIG in management.

Pleconaril, an enterovirus replication inhibitor has been studied and may shorten illness duration but results are mixed and it is not yet a recommended therapy.

What other considerations exist for patients with poliomyelitis or post-poliomyelitis syndrome?

All relevant considerations have been discussed elsewhere.

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