Diseases Mainly Affecting the Long Tracts of the Spinal Cord

The diseases described up to this point affect both the gray and the white matter of the spinal cord. Other diseases of the spinal cord remain confined to the white matter, primarily involving one or more of its long tracts. The origin of these diseases is genetic in many patients (e. g., the spinocerebellar ataxias) but can also be metabolic (e. g., vitamin B12 deficiency), endocrine, paraneoplastic, or infectious.

Hereditary Diseases of the Long Tracts

of the Spinal Cord

Some of the spinocerebellar ataxias have already been described above in Chapter 6 (p. 136); there are a number of other diseases that mainly affect the long tracts of the spinal cord. Their pathophysiology is well understood in only a few patients, not (yet) understood in others.

Friedreich Ataxia

diminution or loss of intrinsic muscle reflexes;

impaired proprioception;

in advanced stages of the disease, cerebellar dysarthria.

Diagnostic evaluation. The diagnosis is based on the typical symptoms and signs. Physical examination characteristically reveals the following:

a typical deformity of the foot due to the pathological abnormality of muscle tone (Fig. 7.13),

intracardiac conduction abnormalities,

often kyphoscoliosis,

sometimes optic nerve atrophy, nystagmus, pyramidal tract signs, and distal muscle atrophy,

psychopathological changes tending toward dementia.

Course. Friedreich ataxia is chronically progressive and causes invalidism within a few years of onset. It sometimes takes a protracted course.

Treatment. No effective treatment is known.

This autosomal recessive hereditary disease is due to a defect on chromosome 9. Its major pathological findings include cell loss in the dentate nucleus and combined degeneration of the spinocerebellar tracts, pyramidal tracts, and posterior columns.

Clinical manifestations. The disease usually becomes manifest in the second decade, initially through signs of posterior column degeneration and then through spasticity and cerebellar signs. Typical findings include:

progressive (spinal) ataxia with disequilibrium, particularly when walking with the eyes closed;

Fig. 7.13 The typical foot deformity in Friedreich ataxia (“Friedreich foot”).

Familial Spastic Spinal Paralysis

This genetically heterogeneous syndrome can be inherited in X-linked, autosomal dominant, or (most commonly) autosomal recessive fashion. Its pathophysiological hallmark is degeneration of the pyramidal tracts, more severe at caudal levels, due to diffuse loss of neurons in the primary motor cortex. This condition is thus caused by isolated disease of the first (upper) motor neuron, as opposed to the spinal muscular atrophies, which involve isolated disease of the second (lower) motor neuron (as will be described further below). Clinically, spastic spinal paralysis is characterized by spastic paraparesis, usually beginning in childhood and then progressing slowly over many years, with exaggerated reflexes, pyramidal tract signs, and increasing gait impairment (“scissors gait” due to adductor spasticity).

Nongenetic Diseases of the Long Tracts

of the Spinal Cord

Funicular myelosis is caused by vitamin B12 deficiency. The latter, in turn, may be due either to inadequate dietary intake or to impaired resorption, owing to a lack of sufficient gastric intrinsic factor (e. g., in atrophic gastritis, or after gastrectomy). The pathological findings include demyelination of the posterior columns, posterior roots, and pyramidal tracts; in later stages of the disease, other tracts of the spinal cord, and the cerebral white matter, can be affected as well. There is often, but by no means always, an accompanying hyperchromic, megaloblastic anemia with macrocytosis, and the patient’s skin is pale yellow. Neurological examination reveals an ataxic gait, impaired proprioception, and, rarely, other sensory deficits. These abnormalities may arise subacutely (over a few weeks) or acutely (over a