Tests
Table 10. Tests to Consider for Patients with Suspected Peripheral Neuropathy | ||
Test | Indications | Interpretation |
Laboratory | ||
CBC, erythrocyte sedimentation rate | Conduct in most patients | Commonly abnormal in systemic disease. Erythroblastic anemia suggests vitamin B12 or folate deficiency; erythrocyte stippling suggests lead toxicity. |
Blood sugar, hemoglobin A1C | Suspected diabetic PN Undiagnosed PN | Symptoms of neuropathy may be the first presentation of diabetes mellitus |
Blood chemistry battery (e.g., SMA 20) | Conduct in most patients | Detects renal insufficiency and other metabolic disorders |
Vitamin B12 levels | Conduct in most patients Suspected nutritional PN |
CNS and posterior-column manifestations may obscure PN; folate treatment normalizes CBC, but does not prevent progressive neurologic injury |
Serum protein electrophoresis | Conduct in most patients | If a paraprotein is identified, request a bone survey and consider bone biopsy to rule out multiple myeloma or osteosclerotic myeloma. |
Serum creatinine kinase (CK) | Suspected motor-neuron disease (MND) | Moderate CK elevation is often supportive of MND diagnosis [6] |
Serologic testing for syphilis, HIV, Lyme disease; tuberculin skin test; antinuclear antibodies; urine tests for aminolevulinic acid, porphobilinogen; urine immunoelectrophoresis; 24-hr urine test for heavy metals (Pb, TI, As) | In selected patients with suggestive clinical indications | Yield is very low in the absence of specific clinical indications |
Cerebral spinal fluid examination | May be particularly helpful in patients with predominant sensory neuropathy, with or without corticospinal findings, and in paraneoplastic neuropathies [5] | CSF protein will be elevated in >90% of patients with acute and chronic inflammatory demyelinating polyneuropathy; it is also frequently elevated in paraneoplastic sensory neuropathy [21]. Elevated total protein with <5 cells/mm3 suggest Gullain-Barré syndrome or chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). |
Radiologic | ||
MRI | Suspected nerve compression (e.g., carpal tunnel syndrome) | Used primarily to confirm peripheral-nerve entrapments/compressions or root disease |
Invasive | ||
Nerve biopsy | Considered when there is a specific diagnosis in mind or when no etiology is evident from serologic and electrodiagnostic tests | Diagnostic abnormalities present in [2]: Vasculitis Amyloidosis Sarcoidosis Leprosy Hereditary neuropathy with liability to pressure palsies Giant axonal neuropathy Metachromatic leukodystrophy Paraproteinemic neuropathy Tumor infiltration |
Based on Bosch [2], Logigian [5], Barohn [6]. |
Table 11. Electrodiagnostic Studies: Key Measurements | |||
Study | Key measurement | Nerves measured | Important parameters |
Motor conduction | Compound muscle action potential (CMAP) | Ulnar Median Peroneal Posterior tibial |
Latency Amplitude Conduction velocity F wave H reflex |
Sensory conduction | Sensory-nerve action potential (SNAP) | Ulnar Median Radial Sural |
Latency Amplitude |
Needle electromyography | Configuration and size of individual motor unit potentials | Not relevant | Spontaneous activity Firing pattern |
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