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Such diseases include a spectrum of disorders in which lesions may be widely disseminated or may more specifically affect certain tracts or cell groups. Examples include: poliomyelitis (viral) which attacks anterior horn cells; amyotrophic lateral sclerosis (etiology unknown) in which anterior horn cells as well as the corticospinal tracts are involved; tabes dorsalis (syphilis due to a spirochete infection) where there is involvement of the posterior white columns and the dorsal roots; posterolateral sclerosis (a nutritional deficiency disease associated with pernicious anemia) involving the corticospinal tracts and posterior white columns; Friedreich's ataxia (an hereditary disorder) shows degenerative changes of the posterior columns, spinocerebellar tracts, lateral white funiculus and cerebellum.

A Sample Case: In the days before the polio vaccine, a 9 year old boy developed fever, headache, malaise, stiff neck, and increasing weakness of the left arm. He was admitted to the hospital where examination revealed nuchal rigidity, a flaccid paresis with muscle fasciculation, hypotonia and hyporeflexia of the left upper extremity which was most pronounced in the biceps and deltoid muscles. Clinical diagnosis was poliomyelitis with involvement limited to the anterior horn cells on the left side, principally in the C-5,6 segments of the cord.

Explanation -

Flu-like symptoms of increased temperature, muscle ache, headache, sore throat, etc., may accompany the initial phase of the viral infection. After subsiding, these initial signs may recur along with the CNS symptoms. Stiffness of the neck on forward flexion (nuchal rigidity) indicates inflammation of the meninges. These preparalytic signs may resolve without further incident. However, muscle weakness may occur during the fever stage; the weakness may be limited to the spinal cord as in this case or also involve the brainstem. Lower motor neuron signs, e.g., coarse fasciculations are seen as the muscles weaken; atrophy and hypotonia are detectable within 3 weeks of onset due to the killing of anterior horn cells.