Critical Care Medicine

Neuromuscular Weakness in Children: Myelitis

Myelitis

Synonyms

Poliomyelitis

Transverse myelitis

Myelopathy

1. Description of the problem

What every clinician needs to know

Myelitis is a useful but generic term to denote inflammation within the spinal cord. The etiology can be direct invasion of spinal cord parenchyma by infectious pathogens or an autoimmune process triggered by remote infection or other events. Conventionally, myelitis implies direct infection, while the term transverse myelitis evolved to distinguish potentially contagious poliomyelitis from the sporadic autoimmune disease that posed no public health risks.

The neurological idiom poliomyelitis came into use more than a century ago and was based on the neuropathological finding of inflammation within the grey matter of the spinal cord. The poliomyelitis virus, now mercifully rare, migrates from the primary site of infection in the GI tract to the anterior grey matter of the spinal cord, where it selectively infects lower motor neurons, resulting in flaccid paralysis. Hence the inclusion of a spinal cord disease in a section on neuromuscular disorders.

By contract, autoimmune transverse myelitis attacks myelinated white matter tracts within the spinal cord, interrupting efferent signals from the cerebral motor cortex and ascending sensory information from peripheral sensory organs. The specific patterns of functional involvement, in some cases, permit discrimination between the two disorders based on clinical findings.

The most useful indicator is the presence of a discrete sensory level corresponding to a spinal dermatomal distribution. Similarly, cranial nerve involvement is not uncommon in poliomyelitis and removes transverse myelitis from the differential diagnosis.

2. Emergency management

The immediate goals are analgesia and prevention of airway or respiratory insufficiency. Narcotic analgesics are almost always necessary for pain relief even though sedative side effects may blunt protective airway reflexes and respiratory drive. Other than supportive care, no specific treatment is available for the most common pathogens responsible for paralytic poliomyelitis.

Especially among those patients with bulbar weakness due to brainstem involvement, dysautonomic symptoms may become problematic. While pulse and blood pressure can be carefully monitored, insensate water loss is more difficult to quantitate.

Exacerbated by the increased surface area:volume ratio, small children can lose large amounts of free water through diaphoresis. The combination of hyperthermia, hypovolemia and dysautonomia can create a perfect storm of hemodynamic instability with unfortunate consequences.

Early intervention to prevent complications of immobility will pay dividends later. As noted above, rehabilitation begins in the ICU. Because of the nature of the primary lesion caused by anterior horn cell injury in poliomyelitis, the resulting acute denervation of muscle results in flaccid paralysis. When paralysis is extensive, there can be rapid and severe bone demineralization with risk for nephrocalcinosis. Acidification of the urine may be necessary to avert this complication.

Public health policy and common sense underscore the urgency in anticipating the potentially transmissible, infectious nature of this neurological disease and taking appropriate precautions for isolation. Similarly, diagnosis requires a coordination of efforts to organize obtaining, processing and distribution of specimens to appropriate diagnostic facilities.

3. Diagnosis

The classical presentation of paralytic spinal poliomyelitis is prodromal malaise, headache and nuchal rigidity followed by the evolution of acute asymmetrical pain and weakness involving legs more often than arms and proximal more than distal muscles. A single extremity may be involved. The affected muscles, themselves, are extremely painful and tender to palpation.

The phrenic nerve nuclei lie within the C2-C5 spinal levels; therefore, when deltoid and other C4-5 muscles are affected, there is considerable risk of ipsilateral diaphraghmatic paralysis. Bulbar involvement results in facial and pharyngeal weakness with pharyngeal incoordination, palatal insufficiency, hoarseness due to vocal cord paralysis and respiratory failure from involvement of ventilatory centers in the medulla. On occasion, the virus will involve more rostral regions, resulting in a clinical picture of encephalitis manifested by encephalopathy and seizures.

Once the paralytic phase of the illness begins, usually within the first 5-7 days of symptoms, weakness evolves rapidly over a 2-3 day course. The muscles become flaccid and tendon reflexes become diminished or disappear entirely. Despite pain, sensory modalities can be demonstrated to be intact.

Pathophysiology

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Epidemiology

Fortunately, epidemic poliomylelitis has been largely eradicated in industrialized nations due to wide-spread immunization programs. Sporadic cases are reported in non-immunized individuals who encountered the wild-type virus. Clustered outbreaks have also occurred among groups that, for sectarian reasons, refuse immunization.

Rare cases have also been noted in unimmunized contacts of children receiving live attenuated-virus vaccines where the attenuated species has mutated into a wild-type pathogen capable of infecting unprotected contacts.

Other viruses are capable of producing a poliomyelitis-like syndrome, including enteroviruses and arboviruses. The two most common offenders are enterovirus 71 and West Nile virus. Both usually occur in an epidemic pattern, the former causing a typical exanthem in a hand-foot-and mouth disease pattern which is benign in the majority of those infected with the virus.

The West Nile virus generally produces a flu-like syndrome which is manifested in humans at a time when the natural host, predominantly birds, and the vector, several species of mosquito, are plentiful in the environment. Neurological involvement occurs in less than 1 % of individuals infected with the West Nile virus.

Prognosis

The prognosis for children who contract paralytic disease due to infection with the polio virus is generally good, with more than 80% making a complete recovery. Limited data from outbreaks of enterovirus-71 and West Nile virus suggest a somewhat less rosey outlook; however, cautious optimism is still warranted in counseling the parents.

Special considerations for nursing and allied health professionals.

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What's the evidence?

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