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Opsoclonus myoclonus syndrome

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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 2 to 3 % of children with neuroblastoma.

Contents

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:

Signs and symptoms

Symptoms include: 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 (6 to 36 months), a diagnosis can be slow. Some cases have been misdiagnosed as having been caused by a virus or conditions such as cerebellar ataxia. After a diagnosis of OMS is made, an associated neuroblastoma is discovered in half of cases, with median delay of 3 months.

Cause

About half of all cases are associated with neuroblastoma and most of the others are suspected to be associated with an low-grade neuroblastoma that spontaneously regressed before detection. It is one of the few paraneoplastic (meaning indirectly caused by cancer') syndromes that occurs in both children and adults, although the mechanism of immune dysfunction underlying the adult syndrome is probably quite different.

It is hypothesized that a viral infection (perhaps St. Louis encephalitis, Epstein-Barr, Coxsackie B, or enterovirus) causes the remaining cases, though a direct connection has not been proven.

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.

Prognosis

Currently there are no clinically established laboratory investigations available to predict prognosis or therapeutic response.

Tumors in children who develop OMA tend to be more mature, showing favorable histology and absence of n-myc oncogene amplification than similar tumors in children without symptoms of OMA (Cooper et al., 2003). Involvement of local lymph nodes is common, but these children rarely have distant metastases and their prognosis, in terms of direct morbidity and mortality effects from the tumor, is excellent (Gesundheit et al., 2004). The three-year survival rate for children with non-metastatic neuroblastoma and OMA was 100% according to Children’s Cancer Group data (gathered from 675 patients diagnosed between 1980 to 1994); three-year survival in comparable patients with OMA was 77% (Rudnick et al., 2001). Although the symptoms of OMA are typically steroid-responsive and recovery from acute symptoms of OMA can be quite good, children often suffer lifelong neurologic sequelae that impair motor, cognitive, language, and behavioral development (Dale, 2003; Mezey and Harris, 2002).

Most children will experience a relapsing form of OMA, though a minority will have a monophasic course and may be more likely to recover without residual deficits (Mitchell et al., 2005). Viral infection may play a role in the reactivation of disease in some patients who had previously experienced remission, possibly by expanding the memory B cell population (Armstrong et al., 2005). Studies have generally asserted that 70-80% of children with OMA will have long-term neurologic, cognitive, behavioral, developmental, and academic impairment. Since neurologic and developmental difficulties have not been reported as a consequence of neuroblastoma or its treatment, it is thought that these are exclusively due to the immune mechanism underlying OMA (Hayward et al., 2001).

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:

A more detailed summary of current treatment options can be found at http://www.omsusa.org/pranzatelli-medications.htm.

The following medications should probably be avoided:

References



External links










 




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