5) DEGENERATIVE DISEASES - POSTEROLATERAL SCLEROSIS
A Sample Case:A 43 year old woman complained of increasing weakness of the legs and difficulty walking which developed over a period of 9 months. She felt numbness and tingling (paresthesia) in her hands and feet.
The neurologic exam revealed loss of position and vibratory sense in both lower extremities. The patient stood and walked clumsily on a wide base and demonstrated the Romberg sign. There was paresis in the lower extremities, with hypertonia, hyperreflexia, and positive Babinski signs. Obvious motor signs in the upper limb were not demonstrated.
Lab studies indicated anemia and a blood smear showed large RBCs (macrocytes). Studies of stomach contents showed a small volume of gastric secretions and a higher than normal pH. The Schilling test, measuring absorption of vitamin B12, showed a decrease.
Neurologic findings of faulty proprioception and paresthesia indicate involvement of the posterior white columns; motor findings indicating upper motor neuron disease implicate the corticospinal tract.
The pathology is diffuse, usually symmetrical, and sometimes involves the legs before the arms. There is degeneration of myelin sheaths followed by death of the axons. These changes are scattered irregularly and usually begin in the cervical and upper thoracic segments and then spread up and down the cord.
Laboratory findings of megaloblastic anemia suggest the disease of pernicious anemia. This is usually caused by an atrophic gastric mucosa which fails to secrete intrinsic factor resulting in failure to absorb sufficient quantities of vitamin B12 as required for effective erythropoiesis. B12 is also an important co-factor in synthesis of fatty acids, important building blocks of cell membranes and hence myelin; this may be the basis of the neurologic findings.