Early in the course of the illness, when only paresthesia is present, there may be no objective sign. Later, examination discloses a disorder of the posterior and lateral columns of the spinal cord, predominantly of the former. Loss of vibration sense is the most consistent sign; it is more pronounced in the feet and legs than in the hands and arms and frequently extends over the trunk. Position sense is usually impaired in parallel. The motor signs, usually limited to the legs, include a mild symmetrical loss of strength in proximal limb muscles, spasticity, enhanced tendon reflexes, clonus, and extensor plantar responses. At first, the patellar and Achilles reflexes are diminished as frequently as they are increased; they may even be absent. This is most likely the result of a neuropathy due to multiple vitamin deficiencies as cases of pure cobalamin loss, for example due to nitrous oxide, almost never obliterate the tendon reflexes. This controversy regarding the presence of a polyneuropathy as a component of SCD has already been alluded to. The gait at first is predominantly ataxic, later ataxic and spastic.
Loss of superficial sensation below a segmental level on the trunk should suggest an alternative diagnosis involving the spinal cord. However, 2 of our patients have described a band-like sensation around the thorax. A defect of cutaneous sensation may take the form of impaired tactile, pain, and thermal sensation over the limbs in a distal distribution, implicating the small fibers of the peripheral nerves or the spinothalamic tracts, but such findings are relatively uncommon. The Lhermitte phenomenon (paresthesia down the spine or across the shoulders induced by rapid flexion of the neck) may be reported by some patients but is more often allied with multiple sclerosis. The nervous system involvement in SCD is roughly symmetrical and distal, and sensory disturbances precede the motor ones; predominantly motor involvement from the beginning and a definite asymmetry of motor or sensory findings maintained over a period of weeks or months or prominent truncal or facial symptoms should always cast doubt on the diagnosis.
Cognitive symptoms and signs are frequent, ranging from irritability, apathy, somnolence, suspiciousness, and emotional instability to a marked confusional or depressive psychosis or dementia. Lindenbaum and coworkers have reported cases in which neuropsychiatric symptoms, responsive to vitamin B12, were present without spinal cord or peripheral nerve abnormalities. In our clinical material, symptoms of dementia or psychosis have not been frequent and always followed the spinal cord disorder. Perhaps a slight degree of mental illness is all that is seen in early stages.
Visual impairment caused by optic neuropathy occasionally may be an early or sole manifestation of pernicious anemia; examination discloses roughly symmetrical centrocecal scotomata and optic atrophy in the most advanced cases. That visually evoked potentials may be abnormal in vitamin B12-deficient patients without clinical signs of visual impairment suggests that the visual pathways are affected more often than is evident from the neurologic examination alone. A small number of patients have symptoms of autonomic dysfunction, including urinary sphincteric symptoms and impotence.
The CSF is usually normal; in some cases there is a moderate increase in protein. The nerve conduction studies may show slowing of sensory conduction or reduced-amplitude sensory potentials, but they are as often normal in early cases. Frequently, according to Hemmer and colleagues, somatosensory evoked potentials are delayed or absent; these changes are known to recover with treatment. Quite remarkable in corresponding to the locus of pathologic change, as these and other authors have indicated, is the finding on MRI of a T2 hyperintensity that demarcates the posterior columns of the cord and sometimes the lateral columns, as shown in Fig. 40-3. In a few of our patients these have taken the form solely of well-defined linear changes over a long extent of the posterior columns of the cervical cord.