Cause
In children, most cases are associated with neuroblastoma and most of the others are suspected to be associated with a low-grade neuroblastoma that spontaneously regressed before detection. In adults, most cases are associated with breast carcinoma or small-cell lung carcinoma. 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, Chikungunya, Epstein-Barr, Coxsackie B, enterovirus, or just a flu) causes the remaining cases, though a direct connection has not been proven. Rare cases of Opsoclonus myoclonus syndrome associated with Lyme disease have also been reported.OMS is not generally considered an infectious disease. OMS is not passed on genetically. 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 diagnosed as having been caused by a virus. After a diagnosis of OMS is made, an associated neuroblastoma is discovered in half of cases, with median delay of 3 months.The interictal EEG pattern is usually normal. Treatment
There is no known definitive cure for OMS. However, several drugs have proven to be effective in their 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.
Evinacumab, sold under the brand name Evkeeza, is a monoclonal antibody medication for the treatment of homozygous familial hypercholesterolemia (HoFH).Common side effects include nasopharyngitis (cold), influenza-like illness, dizziness, rhinorrhea (runny nose), and nausea. Serious hypersensitivity (allergic) reactions have occurred in the Evkeeza clinical trials.Evinacumab binds to the angiopoietin-like protein 3 (ANGPTL3). ANGPTL3 slows the function of certain enzymes that break down fats in the body. Evinacumab blocks ANGPTL3, allowing faster break down of fats that lead to high cholesterol. Evinacumab was approved for medical use in the United States in February 2021.Regeneron invented evinacumab using the companys VelocImmune® technology, a proprietary genetically-engineered mouse platform endowed with a genetically-humanized immune system to produce optimized fully-human monoclonal antibodies. History
The effectiveness and safety of evinacumab were evaluated in a double-blind, randomized, placebo-controlled, 24-week trial enrolling 65 participants with homozygous familial hypercholesterolemia (HoFH). In the trial, 43 participants received 15 mg/kg of evinacumab every four weeks and 22 participants received the placebo. Participants were taking other lipid-lowering therapies as well.The primary measure of effectiveness was the percent change in low-density lipoprotein (LDL-C) from the beginning of treatment to week 24. At week 24, participants receiving evinacumab had an average 47% decrease in LDL-C while participants on the placebo had an average 2% increase.The U.S. Food and Drug Administration (FDA) granted the application for evinacumab orphan drug, breakthrough therapy, and priority review designations.