Opsoclonus myoclonus syndrome is a very rare condition, considered to be an autoimmune condition, the cause of which is still unclear. However, they occur more in children between 1 to 2 years of age and is very commonly associated with neuroblastoma. In case of adults it is commonly associated with some carcinoma. You have not specified your girl s age. There is also no well established treatment guideline of the condition. However, steroid and iv ig are commonly used to halt the disease progression. However, there is no confirmatory evidence regarding betterment of these patients after treatment with naltrexone. There have been discussions going on regarding the use of naltrexone in different autoimmune diseases including OMS. But, still it is controversial. Regarding the tests, if you are talking about serotonin receptors, I can say that they are now being studied to be used as a tumour marker for this and many other conditions. As she is already being treated for the condition after having been diagnosed provisionally, a better option is to rule out the above mentioned conditions that are commonly associated with the disease. Regarding any test to know whether your daughter is immunocompromised different tests are there including ratio of CD 4 and CD 8 cells. However, I don t think that would be needed at this point of time. She is already being treated to suppress the immune system so that they don t fight against body s own cells. Furthermore, I am very sorry to declare that as per the current status, we don t know an established cure for the disease. Please consult your doctor and follow his advices. There is no need to do unnecessarily costly test which will not provide any extra information that can help in the treatment or prognosis. For any further information, please write back to us. Regards. Dr. Kaushik