Neuropathy refers to dysfunction of the peripheral nerve. It often presents with progressive pain and/or numbness. The EMG study shows decreased amplitude in the SNAPs (sensory nerve action potentials). This form of neuropathy is usually due to a toxic-metabolic insult such as chemotherapy, diabetes or chronic alcohol use. Sometimes it is the result of connective tissue diseases such as lupus, polyarteritis nodosa or Sjogren’s syndrome. All of these conditions have to be screened for in any evaluation. Sometimes no cause is found and treatment is symptomatic.
There is another very common neuropathic condition seen almost exclusively in the elderly, and it present with progressive imbalance. It is called CIDP (chronic immune demyelinating polyneuropathy) and is an autoimmune condition where there is a loss of myelin in the peripheral nerve. Myelin is the fatty tissue which surrounds every nerve and which enhances conduction. When it is damaged, conduction of electricity in the nerve is slowed. More importantly, different frequencies travel at different velocities (dispersion), the message from the nerve is scrambled, and the brain is no longer sure where the limb is in space. The result is an imbalance. This is a serious condition since it can result in falling, yet it is often highly treatable with intravenous immunoglobulin (ivIg). The EMG signature is slowing of nerve conduction.
CIDP is not usually associated with monoclonal proteins but sometimes it is. These must be screened for with a blood test known as immune protein electrophoresis since a monoclonal spike in the blood could represent a more malignant underlying condition such as multiple myeloma or lymphoma. If the spike is of the IgG type, then a bone marrow aspiration is mandatory. Usually, this is negative for malignancy and most of these neuropathies are treatable. If it is IgM then it is usually benign but is usually less responsive to ivIg.