How should ocular myoclonus be evaluated and treated?

Evaluation and Management of Ocular Myoclonus

When a patient presents with abnormal eye movements that appear myoclonic, immediately determine whether this represents true opsoclonus-myoclonus syndrome (OMS) versus isolated myoclonus, as OMS demands urgent malignancy screening and immunotherapy consideration.

Initial Clinical Characterization

Distinguish opsoclonus from other eye movement disorders:

• Opsoclonus consists of chaotic, multidirectional (horizontal, vertical, torsional), back-to-back saccades without intersaccadic intervals 1, 2
• Ocular flutter is the horizontal-only variant of the same phenomenon 2
• These movements are involuntary, rapid, and conjugate saccadic intrusions that oscillate about central fixation 2
• Consciousness remains preserved during episodes, distinguishing this from epileptic events 3

Key associated features to assess:

• Presence of body myoclonus (sudden, brief, lightning-like jerks) suggests OMS rather than isolated ocular flutter 1
• Ataxia and encephalopathy complete the classic OMS triad 1
• Timing: movements occurring within 48-72 hours after cardiac arrest carry prognostic implications but different management 1

Urgent Etiologic Workup

Immediately screen for malignancy based on age:

• Children: Obtain abdominal imaging (CT or MRI) and urine catecholamines to detect neuroblastoma, the most common pediatric cause 1
• Adults: Screen for breast cancer, small cell lung cancer (SCLC), and gynecologic malignancies with chest CT, mammography, and pelvic imaging 1, 4
• The malignancy may be occult, and opsoclonus symptoms often precede tumor detection 5, 4

Obtain infectious and inflammatory workup:

• CSF analysis for lymphocytic pleocytosis (parainfectious causes including dengue, other viral infections) 5, 6
• Serum neuronal surface antibodies (NSAbs): NMDAR-Ab, GlyR-Ab, CASPR2-Ab 1
• Consider GAD antibodies if progressive encephalomyelitis with rigidity features present 1

Perform EEG recording:

• EEG during episodes helps identify epileptiform activity and assess cortical reactivity 1, 3
• Distinguishes cortical myoclonus (with EEG correlate) from subcortical forms (without correlate) 3

Brain and spinal MRI:

• Identify structural lesions, brainstem/cerebellar pathology 3, 2
• OMS mechanism relates to dysfunction of brainstem and cerebellar saccade-generating machinery 2

Treatment Algorithm

For Paraneoplastic OMS:

Tumor removal is the definitive treatment:

• One patient with thymoma had dramatic improvement after surgery plus immunotherapy 1
• Tumor-directed therapy takes precedence over symptomatic management 1

For Idiopathic/Parainfectious OMS:

Initiate immunotherapy based on age and presentation:

• Adult idiopathic OMS (frequently women, monophasic course): Use intravenous immunoglobulins (IVIG) or corticosteroids as first-line 1
• Pediatric non-paraneoplastic OMS: Immunotherapies appear beneficial, though systematic studies are lacking 1
• GlyR-antibody positive cases: These patients respond well to immunotherapies, unlike GAD-antibody cases 1

Conservative management for parainfectious cases:

• Some parainfectious cases (e.g., dengue-associated) show spontaneous improvement by day 5 with complete recovery in 2 weeks 6
• Monitor closely before escalating to immunotherapy if infectious etiology confirmed 6

For Post-Cardiac Arrest Myoclonus:

Do NOT use myoclonus alone for prognostication:

• Status myoclonus within 72 hours after cardiac arrest predicts poor outcome with 0% false positive rate 3
• However, isolated myoclonus has 5-11% false positive rate and must not be used alone 3
• The American Heart Association mandates multimodal prognostication combining pupillary reflexes, corneal reflexes, EEG, and imaging 1, 3
• Evaluate patients off sedation and wait ≥72 hours to minimize false positives from residual medications 1, 3
• Record EEG during myoclonic jerks to detect epileptiform activity 1

Treatment options for post-arrest status myoclonus:

• Sodium valproate, levetiracetam, clonazepam, propofol, benzodiazepines, or barbiturates 3
• Note: No specific AAN guidelines exist, but these agents are used in practice 3

Critical Pitfalls to Avoid

Do not miss occult malignancy:

• Opsoclonus may precede tumor symptoms by weeks to months 5, 4
• Repeat imaging if initial workup negative but clinical suspicion remains high 4

Do not confuse with other movement disorders:

• Tics are suppressible and more complex in pattern 3
• Clonus is rhythmic, sustained, and triggered by muscle stretch—fundamentally different from myoclonus 7
• Convulsive syncope involves movements after loss of consciousness, not as the primary symptom 3

Do not delay immunotherapy in idiopathic adult OMS:

• These patients have good response to IVIG or steroids and typically follow a monophasic course 1
• Early treatment may prevent cognitive sequelae seen in untreated pediatric cases 1

In post-cardiac arrest patients:

• Never use myoclonus as the sole prognostic indicator given the false positive rate 3
• Some patients with early status myoclonus have achieved good neurological recovery, including those who developed Lance-Adams syndrome 1