Opsoclonus myoclonus syndrome

Overview

Opsoclonus Myoclonus Syndrome (OMS), also known as Opsoclonus-Myoclonus-Ataxia Syndrome (OMAS), is a rare neurological disorder characterized by a distinctive triad of symptoms: rapid, involuntary eye movements (opsoclonus), brief, shock-like muscle jerks (myoclonus), and difficulty with coordination and balance (ataxia). The condition is believed to be immune-mediated and can occur as a paraneoplastic syndrome, often associated with neuroblastoma in children, or as a parainfectious or idiopathic condition in adults.

OMS can affect individuals of any age, but it is most commonly diagnosed in children under the age of three. It is considered a neurological emergency due to its rapid onset and potential for lasting cognitive and motor impairments. Early recognition and aggressive immunotherapy significantly improve outcomes.

Causes

Opsoclonus Myoclonus Syndrome is thought to result from an autoimmune response in which the body's immune system mistakenly attacks its own nervous system, particularly targeting the brainstem and cerebellum. The syndrome may be classified based on its underlying trigger:

Paraneoplastic Causes

• Neuroblastoma: The most common cause in children. OMS may be the first sign of an underlying tumor, even when the tumor is small or asymptomatic.

• Other tumors: Rarely, in adults, associated with breast, lung, or ovarian cancers.

Parainfectious and Idiopathic Causes

• Viral infections: Such as Epstein-Barr virus, Coxsackievirus, or influenza.

• Bacterial infections: Including Mycoplasma pneumoniae and others.

• Idiopathic: No identifiable cause in some patients; believed to be autoimmune in nature.

Autoimmune Mechanism

Regardless of the trigger, OMS is believed to involve autoantibodies or immune cells attacking neurons involved in motor control. The precise antigen is not always identified, but the immune dysfunction leads to widespread neurological symptoms.

Symptoms

The clinical presentation of OMS can be dramatic, with symptoms often appearing suddenly and progressing rapidly. The condition is characterized by the following key features:

Core Symptoms

• Opsoclonus: Rapid, involuntary, multidirectional, conjugate eye movements that are chaotic and without intersaccadic intervals.

• Myoclonus: Sudden, brief, involuntary jerks of the limbs, trunk, or face.

• Ataxia: Unsteady gait, difficulty standing or walking, and lack of coordination.

Other Neurological and Behavioral Features

• Irritability and sleep disturbances

• Speech regression or mutism

• Hypotonia: Decreased muscle tone

• Tremors and dystonia

• Cognitive impairment: Learning and memory difficulties

In Children

• Developmental regression: Loss of motor, speech, or social skills

• Behavioral changes: Aggression, temper tantrums, or anxiety

Diagnosis

Diagnosis of OMS is clinical and based on the characteristic symptom triad, supported by neuroimaging, laboratory tests, and tumor screening. Early diagnosis is essential for initiating treatment and minimizing long-term damage.

Clinical Evaluation

• Observation of opsoclonus, myoclonus, and ataxia by a neurologist

• Assessment of developmental history and onset of behavioral symptoms in children

Laboratory and Imaging Studies

• MRI of the brain: Often normal or may show cerebellar atrophy in chronic cases

• CSF analysis: May reveal elevated white cells or oligoclonal bands, indicating inflammation

• EEG: Usually normal or nonspecific, used to rule out seizures

Tumor Screening

• Abdominal ultrasound or CT/MRI: To detect neuroblastoma in children

• MIBG scan (metaiodobenzylguanidine): Highly sensitive for identifying neuroblastoma

• Onconeural antibody panels: In adults, to detect antibodies associated with paraneoplastic syndromes

Treatment

Treatment of Opsoclonus Myoclonus Syndrome focuses on immunosuppression to control the autoimmune response, tumor resection if applicable, and supportive therapies to aid recovery. Early and aggressive treatment improves the likelihood of full or partial recovery.

Immunotherapy

• Corticosteroids: High-dose intravenous methylprednisolone followed by oral tapering regimen

• Intravenous immunoglobulin (IVIG): Often used in conjunction with steroids

• Rituximab: A monoclonal antibody targeting B cells; used in steroid-resistant cases

• Cyclophosphamide: An immunosuppressive agent used in severe or refractory cases

Tumor Treatment

• Surgical resection: Of neuroblastoma or other identified tumors

• Chemotherapy or radiation: If required for complete tumor management

Supportive and Rehabilitative Care

• Physical therapy: To improve motor coordination and strength

• Occupational therapy: For fine motor and daily living skills

• Speech and language therapy: Especially in children with regression

• Psychological counseling: To manage behavioral and emotional issues

Prognosis

The prognosis for Opsoclonus Myoclonus Syndrome varies widely. With early diagnosis and aggressive immunotherapy, many patients—especially children—can experience significant improvement or remission of symptoms. However, some individuals may experience relapses or develop long-term neurological or cognitive deficits.

Favorable Factors

• Early initiation of immunotherapy

• Complete tumor removal (if paraneoplastic)

• Multidisciplinary rehabilitation

Long-Term Outcomes

• Complete remission: Possible in some cases, especially with prompt treatment

• Residual symptoms: Such as mild ataxia, learning difficulties, or behavioral issues

• Chronic OMS: In a minority of cases, symptoms may persist or relapse over time

Ongoing follow-up with neurology, oncology, and developmental specialists is essential to manage relapses, monitor development, and optimize functional outcomes.