Treatment If the tumor can be treated effectively, the neuropathy may improve, the exception being pure sensory neuronopathy, which rarely does so. Treatment with plasma exchange, gamma globulin, or immunosuppression has had only a minimal effect, but there are anecdotal reports of success with each of these treatments applied early in the course. In the report by Uchuya and colleagues, only 1 of 18 patients with a subacute sensory neuropathy improved and another became dependent for sustained improvement on immune globulin; most of the others stabilized or worsened and the authors concluded that treatment was of doubtful value. Corticosteroids have not been tested in a systematic way for paraneoplastic neuropathy and there is little clinical evidence to support their use.
Of the neuropathies caused by metallic poisoning, that caused by arsenic has been particularly well characterized. In cases of chronic poisoning, the neuropathic symptoms develop rather slowly, over a period of several weeks or months and have the same sensory and motor distribution as the nutritional polyneuropathies. Gastrointestinal symptoms, the result of ingestion of arsenic compounds, may precede the polyneuropathy, which is nearly always associated with anemia, jaundice, brownish cutaneous pigmentation, hyperkeratosis of palms and soles, and later with white transverse banding of the nails (Mees lines). The disease is accompanied by an excess of arsenic in the urine and hair. Pathologically, this form of arsenical neuropathy is categorized as of the dying-back (axonal degeneration) type.
In patients who survive the ingestion of a single massive dose of arsenic, a more rapidly evolving polyneuropathy may appear after a period of 8 to 21 days as discussed earlier. Diagnosis and treatment of arsenical poisoning are discussed further in Chap. 41. Here it is emphasized that the ingestion of fish in many areas of the industrialized world gives high levels of blood and urine arsenic, but the metal is in the form of arsenobetaine, which has low toxicity and does not cause neuropathy.
This is an uncommon disorder. In adults, it occurs following chronic exposure to lead paint or fumes (from smelting industries or burning batteries) or from ingestion of liquor distilled in lead pipes. Its most characteristic presentation is a motor mononeuropathy in the distribution of the radial nerves (wrist and finger drop). In a few personally observed patients this was the main abnormality, but there was also a sensory loss in the radial territory of the hand. Less commonly, there is foot-drop occurring alone or in combination with weakness of the proximal arm and shoulder girdle muscles. As pointed out in Chap. 41, lead neuropathy seldom occurs in children, in whom poisoning usually results in an encephalopathy. Although the neuropathy has been known since ancient times, details of the pathobiology are still obscure. Axonal degeneration with secondary myelin change and swelling and chromatolysis of anterior horn cells has been described. Lead accumulates in the nerve and may be toxic to Schwann cells or to endothelial capillary cells, causing edema.
The diagnosis is established by the history of lead exposure, the predominant and restricted motor involvement, associated medical findings (anemia, basophilic stippling of red blood cell precursors in the bone marrow, a “lead line” along the gingival margins, colicky abdominal pain, and constipation), and the urinary excretion of lead and coproporphyrins. Blood lead levels of more than 70 mg/dL are always abnormal. In patients with lower levels, doubling of the 24-h urinary lead excretion following an infusion of the chelating agent CaNa2 ethylenediaminetetraacetic acid (EDTA) indicates a significant degree of lead intoxication. Coproporphyrin in the urine is abnormal in any amount, but it may also be found in porphyria, alcoholism, iron deficiency, and other disorders as well as in lead intoxication.