By Jonathan Katz, MD and co-author Michelle Greer, RN, MBA
Neuropathy means disease or abnormality of the nervous system. Certain types of neuropathies are characterized by conditions in which nerves are “attacked” by the patient’s own immune system. There are several types of inflammatory neuropathies, but the two most common are Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) and Multifocal Motor Neuropathy (MMN).
CIDP causes weakness and sensory abnormalities that usually develop over several months. The disease can stop progressing, and relapses and remissions can occur. The severity of CIDP can vary from mild to severe, and it can affect any age group and either gender. Normally, CIDP is not painful, although some patients complain of unusual or troubling sensations.
MMN is a disorder characterized by weakness and muscle atrophy that usually affects the hands. MMN can cause minimal weakness in just a few muscles, or it may cause relatively severe weakness in all limbs. Because it only affects strength, but not sensation, MMN is sometimes mistaken for ALS (amyotrophic lateral sclerosis), or Lou Gehrig’s disease. Unlike ALS, MMN is an immune neuropathy and responds to the same treatments.
In both MMN and CIDP, the attack occurs against the myelin sheath, which surrounds the nerve and provides insulation for nerve conduction. The attack can also interfere with specialized “ion channels” in nerves that help electrical signals pass up and down the long processes. As a result, electrical impulses that carry the electrical signals are damaged.
The diagnosis of these disorders depends heavily on nerve conduction studies that prove nerve signals are abnormal. They also depend on a complete examination of the nervous system by a specialist who can recognize the unusual patterns of muscle weakness and sensory loss. A lumbar puncture is sometimes needed to check for high protein levels and, in rare cases, a nerve biopsy may be required.
For MMN, a specialized blood test called anti-GM1 antibodies is useful if it is positive. One common treatment for MMN and CIDP is IVIG (intravenous immune globulin). IVIG is FDA-approved for both conditions. Insurance companies often have strict criteria that must be met in order for IVIG to be covered. Many, but not all, cases will improve, and the symptoms will decrease within a few weeks to a few months after IVIG is started. IVIG is given at intervals ranging from every two weeks to every other month. Responses tend to wear off, so treatments need to be repeated.
Because diagnosis can be difficult, some doctors consider the first few treatments with IVIG as part of the diagnosis. Patients who do not respond probably have a different type of neuropathy. Since IVIG is also very expensive, and the diseases can stabilize, it is important that the neurologist check for responses regularly to determine whether ongoing treatments are needed and what doses are necessary.
A steroid called prednisone is often used to treat CIDP as well. Prednisone causes more side effects than IVIG but also works well to treat the disease. Prednisone cannot be used for MMN, since it does not work for that particular neuropathy. There are other medications that can treat immune neuropathy, and these may be used when the condition is severe.
In our next blog, we will explore what patients should expect during a complete neurological exam and workup.