Dr. Jeff Hersh: What is Devic’s disease?
Q: What is Devic’s disease? Is it a kind of multiple sclerosis?
A: Doctors Devic and Gault first described Devic’s disease (now called neuromyelitis optica or NMO) in 1894 from their experience with 16 patients. NMO is a rare disease of the central nervous system, affecting about 4000 Americans every year. It can affect anyone, but is much more common in women than men, with a mean age of onset of about 40.
NMO is an autoimmune disease (the body’s own antibodies attack normal body substances/cells) that causes demyelination (the electrically insulating substance called myelin, which surrounds nerve fibers, is damaged), inflammation and damage of the optic nerve (optic neuritis) and spinal cord (transverse myelitis); it does not affect the brain. The symptoms from attacks (which may become permanent from a “mono-phasic” prolonged attack lasting a month or more, or may cumulate from “poly-phasic” attacks that may occur over the course of months or years) may include:
* Vision loss (sometimes only color vision is lost) and even blindness (which can be rapid in onset) from optic neuritis; a presenting symptom in almost half of patients.
* Weakness and even paralysis of the arms and/or legs (depending on what area of the spinal cord is affected); a presenting symptom in almost half of patients.
* Most NMO patients eventually experience at least some amount of vision loss and extremity weakness.
* Bladder and/or bowel involvement.
* Respiratory compromise (the most common cause of death in NMO patients).
* Intractable hiccups and/or intractable nausea/vomiting (for almost 10 percent of patients this is the initial symptom).
Although NMO was initially thought to be a type of multiple sclerosis (MS), it is now known that it is a separate disease entity, although its symptoms may overlap those of MS. It is different from MS in that:
* No specific antigen (the substance that provokes an immune response) has been identified for MS, but in NMO it is known that normal aquaporin 4 molecules are misidentified as “foreign” cells by the body’s immune system; the NMO-IgG antibody responsible for this autoimmune response has been identified, and is found in 70 percent of patients with NMO but not in MS patients.
* Initial NMO symptoms are generally severe and often cumulative, whereas initial symptoms in MS are often more subtle and usually improve or resolve between attacks (although eventually the symptoms may become permanent).
* Fatigue is a common primary symptom of MS, but for NMO it is usually secondary to other neurological problems the disease causes.
* NMO affects the optic nerve and long segments of spinal cord but does not involve the brain, whereas MS may affect any area of the brain (in fact part of the diagnostic criteria for MS is that it is a disease ‘over time and space’, meaning it affects different areas of the brain at different times over the course of the disease) and when it does affect the spinal cord it is usually shorter segments than in NMO.
Diagnosis of NMO is made based on the symptoms (including the lack of symptoms from other nerve or brain involvement) and at least two of:
* An MRI not showing any brain involvement (as would be seen in MS).
* A positive blood test for NMO antibodies (although 30 percent of patients have an initial negative test).
* An MRI showing a spinal cord lesion extending the length of at least 3 vertebral segments.
There are no specific treatments for NMO, but because it is an autoimmune disease medications that inhibit the immune system are used. Initial treatment for a flare of NMO is often intravenous steroid medications; other immune-modulating medications and/or monoclonal antibodies may be used as well. Since these medications may compromise the effectiveness of the immune system, there is an increased risk of infections as well as certain cancers (for example PML) when their use is required. Medications to treat symptoms (such as pain) are also indicated.
Much has been learned about NMO over the last 10 years. Research is ongoing to hopefully identify effective treatments for this serious disease.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.