How Is Neuropathy Diagnosed?
The diagnosis of neuropathy is based on an in-depth history and a thorough physical exam, including a neurological exam, blood tests, and electrodiagnostic testing. The more obvious the cause, the less necessary are extensive diagnostic procedures. For example, a diabetic patient with foot pain neuropathy may not require a full evaluation that includes nerve conduction studies or electromyography (EMG).
Pertinent Medical History
The onset, progress, nature, and distribution of neuropathy, reported by the patient, can classify the complaints as to the type of neuropathy that is present. Family history can indicate a possible hereditary influence that predisposes an individual. Most importantly, the history is crucial to tell apart the polyneuropathy syndromes (same illness affecting many nerves) from mononeuropathy multiplex (multiple compressions of unrelated nerves). If neuropathic symptoms are from higher up, i.e., the central nervous system, a history can distinguish signs and symptoms of a stroke.
The history also can highlight suspicions of toxicities that cause neuropathy, such as drugs (both prescribed and illicit abuse) and environmental causes (work-related chemical exposure). During the medical history, illnesses that figure prominently in neuropathy are all reviewed, from diabetes to Lyme disease.
The difference between signs and symptoms is that signs are objective observations, such as blood pressure or pulse, whereas symptoms are subjective complaints from the patient, such as tingling. For the diagnosis of neuropathy, the signs are more reliable than symptoms, unless there are many of them that cluster about a common syndrome. Isolated symptoms are not particularly helpful.
Signs during a physical exam, however, take advantage of the fact that the human body is generally symmetric and, with the exception of one’s dominant hand, is generally balanced as to strength. Even taking a dominant hand into account, reflexes and sensitivity to tactile stimuli (pinprick, vibration, temperature, feather, etc.) can easily indicate when one side or one part is weak, hypersensitive, or has decreased sensitivity. These techniques are part of a neurological evaluation during the physical exam.
Since late syphilis results in both central and peripheral neuropathy, a screening test for it is indicated when there are problems with walking; the false positives in the screening can be eliminated with definitive testing for its specific antigen. Hepatitis B and C antigens can be identified. Chronic inflammatory states can be identified by tests for inflammation such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Measurements of heavy metals can be done by testing the blood, as can antibodies associated with neuropathy (hepatitis C, herpes) and vitamin levels. Blood tests are also useful in identifying systemic disease that correlate with neuropathy. Besides the obvious glucose measurements used in diabetes, tests for uremia (kidney illness) can be useful in identifying such a cause or in ruling it out.
Electrodiagnostic testing is indicated when there is suspicion of polyneuropathy, there is no reliable cause elicited from the history and physical exam, or when signs and symptoms progress rapidly or become severe. It is also useful when there is obvious asymmetry or predominantly motor abnormalities (as opposed to sensory). Nerve conduction studies and electromyography can determine conduction speeds of the nerves and can identify partial or complete blocks of the transmission signals.