Opsoclonus myoclonus syndrome (OMS) is a rare neurological disorder of unknown causes which appears to be the result of an autoimmune process involving the nervous system. It is an extremely rare condition, affecting as few as 1 in 10,000,000 people per year. It affects 1 to 3 percent of children with neuroblastoma.
Nomenclature
OMS was first described by Dr. M. Kinsbourne in 1962 (The term 'Opsoclonus' was coined by Orezechowski in 1913, but it was classically described and associated with neuroblastoma by Kinsbourne). Other names for OMS include:
opsoclonus:
myoclonus
ataxia
intention tremor
dysphasia
dysarthria
mutism
hypotonia
lethargy
irritability or malaise
drooling
strabismus
vomiting
Sleep problems ("night rages").
About half of all OMS cases occur in association with neuroblastoma.
Diagnosis
Because OMS is so rare and occurs at an average age of 19 months, a diagnosis can be slow. Some cases have been misdiagnosed as having been caused by a virus or conditions such as cerebellar ataxia.
Cause
The ultimate cause of OMS is unknown. About half of all cases are associated with neuroblastoma and most of the others are suspected to be associated with an undetected neuroblastoma. It is hypothesised that a viral infection causes the remaining cases, and probably most or all of the adult cases. Certainly OMS is not an infectious disease. OMS is not a passed on genetically.
Disease course and clinical subtypes
In most cases OMS starts with an acute flare-up of physical symptoms within days or weeks, but some less obvious symptoms such as irritability and malaise may begin weeks or months earlier.
Factors triggering a relapse
Infections have been reported to increase the risk for a relapse.
Prognosis
Currently there are no clinically established laboratory investigations available to predict prognosis or therapeutic response.
One study (Medical and Pediatric Oncology 36:612-622,2001, see below) came to the conclusion that:
Patients with OMA and neuroblastoma have excellent survival but a high risk of neurologic sequelae. Favourable disease stage correlates with a higher risk for development of neurologic sequelae. The role of anti-neuronal antibodies in late sequelae of OMS needs further clarification.
Another study (Neuroepidemiologic Trends in 105 US Cases of Pediatric Opsoclonus-Myoclonus Elizabeth D. Tate, Michael R. Pranzatelli, Tyler Allison, Steven Verhurst, Springfield, IL states that:
Residual behavioral, language, and cognitive problems occurred in the majority.
Treatment
There is no known definitive cure for OMS. However, several drugs have proven to be effective in its treatment.
Some of medication used to treat the symptoms are:
ACTH has shown improvements in symptoms but can result in an incomplete recovery with residual deficits.
corticosteroids (such as prednisone or methylprednisolone) used at high dosages (500 mg - 2 g per day intravenously for a course of 3 to 5 days) can accelerate regression of symptoms. Subsequent very gradual tapering with pills generally follows.
Immunoglobulins (antibodies) are often used with varying results.
Several other immunosuppressive drugs, such as cyclophosphamide, may be helpful in some cases.
Chemotherapy for neuroblastoma may sometimes be effective.
Rituximab has been used with encouraging results. See Immunologic and Clinical Responses to Rituximab in a Child With Opsoclonus-Myoclonus Syndrome Michael R. Pranzatelli, MD, Elizabeth D. Tate, FNP-C, MN, Anna L. Travelstead, BS, MT(ASCP)§ and Darryl Longee,MD
Methotrexate has been used. This drug has also been found very helpful in treating rheumatoid arthritis, although its mechanism of action in this illness is not known. It seems to work, in part by altering aspects of immune function which may play a role in causing rheumatoid arthritis and OMS.
Other medications are used to treat symptoms without influencing the nature of the disease (symptomatic treatment):
Tradazone can be useful against irritability and sleep problems
Additional treatment options include plasmapheresis ("washing the blood", showing similarities to dialysis) for severe, non-steroidresponsive relapses.
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