| 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-Barre 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 |