Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (90 page)

   EBV (mononucleosis associated: CSF shows increased protein and up to several hundred mononuclear cells)

   Lyme disease

Additional laboratory information that may be contributive:

   Serum and urine for toxicity to drugs and chemicals (lead, arsenic, etc.)

   Blood tests for vitamin deficiencies, pregnancy, and porphyria

Biopsy:

Nerve biopsy may be useful in diagnosing the underlying cause of the neuropathy especially in cases that are difficult to differentiate between axonal and demyelinating etiologies. Nerve biopsy may also help to diagnose amyloidosis, leprosy, vasculitis, and sarcoidosis.
²
Skin biopsy may be helpful in disorders that affect small unmyelinated nerve fibers, such as in pain, numbness, and paresthesias.
³

References

1.  England JD, Gronseth GS, Franklin G, et al. Practice Parameter: evaluation of distal symmetric polyneuropathy: role of laboratory and genetic testing (an evidence-based review). Report of the American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Academy of Physical Medicine and Rehabilitation.
Neurology.
2009;72:185.

2.  England JD, Asbury AK. Peripheral neuropathy.
Lancet.
2004;363:2151.

3.  McCarthy BG, Hsieh ST, Stocks A, et al. Cutaneous innervation in sensory neuropathies: evaluation by skin biopsy.
Neurology.
1995;45:1848.

DIABETIC POLYNEUROPATHY

   Definition

Diabetic polyneuropathy is primarily a symmetrical neuropathy affecting the distal lower extremities. There is loss of vibratory sensation and impairment of pain, light touch, and temperature sensation.
¹

   Clinical Presentation

Patients with diabetes may present with a number of different neuropathies including symmetric polyneuropathy, autonomic neuropathy, radiculopathies, mononeuropathies, and mononeuropathy multiplex.

   Laboratory Findings

The differential diagnosis includes metabolic disorders such as uremia, folic acid deficiency, hypothyroidism, and acute intermittent porphyria. Other entities in the differential should include alcohol, heavy metal toxicity, and exposure to hydrocarbons. Collagen vascular diseases such as periarteritis nodosa and lupus may also cause symmetric polyneuropathy. Also in the differential is infection with leprosy or inflammatory disorders such as sarcoidosis. Rare disorders including paraneoplastic syndromes, hematologic malignancy, amyloidosis, and hereditary neuropathies may also be considered.

In a patient with known diabetes, the diagnosis is based on clinical findings and physical examination using one of a number of testing tools.
^2,3
When the presentation is atypical electrodiagnostic, testing may be helpful. Laboratory testing should include screening to rule out vitamin B
₁₂
deficiency, hypothyroidism, and uremia.

References

1. Partanen J, Niskanen L, Lehtinen J, et al. Natural history of peripheral neuropathy in patients with non-insulin-dependent diabetes mellitus.
N Engl J Med.
1995;333:89.

2.  Dyck PJ, Kratz KM, Lehman KA, et al. The Rochester Diabetic Neuropathy Study: design, criteria for types of neuropathy, selection bias, and reproducibility of neuropathic tests.
Neurology.
1991;41:799.

3.  Dyck PJ, Albers JW, Andersen H, et al. Diabetic polyneuropathies: update on research definition, diagnostic criteria and estimation of severity.
Diabetes Metab Res Rev.
2011, Jun 21. doi: 10.1002/dmrr.1226. [Epub ahead of print]

CRANIAL NERVE NEUROPATHY, MULTIPLE

   Definition

Neuropathies of the cranial nerves are most commonly due to local compression of the nerve by trauma, infection, or tumor; vascular and collagen vascular disorders; and some metabolic diseases.

   Laboratory Findings

Laboratory findings may be helpful to determine the underlying etiology:

   Peripheral blood for glucose, HgbA1c, BUN, creatinine, AST, and ALT may reveal a metabolic disorder (DM, renal failure, chronic liver disease, myxedema, and porphyria).