CMET-24. PLATEAU WAVE EVENTS: A COMMON, CURABLE, AND ROUTINELY MISDIAGNOSED SYNDROME IN PATIENTS WITH NEOPLASTIC MENINGITIS (NM)

INTRODUCTION NM is defined clinically by multilevel neurologic dysfunction. Seizures occur in less than 15% of patients. We describe a curable phenomenon (“plateau wave events”) that mimics and may be more common than seizures, but is not responsive to anticonvulsant medication. METHODS We queried a multinational NM registry to identify patients with episodic neurologic dysfunction suspected of having seizures. Detailed demographic, disease, treatment, and outcome data were collected. RESULTS Forty-three patients (21.2% of 203) were identified. Twenty patients (46.5% of 43) demonstrated a stereotyped constellation of symptoms including episodic severe headache and loss (19 patients) or impaired level (1 patient) of consciousness, nausea, vomiting, and gait instability lasting 30–180 seconds, with abrupt resolution and without post-ictal symptoms. Events developed a median of 74 (0–350) days following NM diagnosis. Fourteen patients (74%) were female. Median age was 54.8 [IQR 46.8, 61.6] years. Fourteen patients had solid tumors (11 breast), 5 had hematologic malignancies, and 1 had a primary brain tumor. Thirteen (68%) had ventriculomegaly. All patients demonstrated increased ICP [median 30.0 cm H2O, IQR 22.5, 30.0]. CSF cytology was positive and CSF protein was increased in 100% of patients, but no demographic, laboratory, or disease characteristic was associated with plateau wave events on multivariate analysis. Inter-ictal EEG in 8 patients showed no epileptiform activity. One intra-ictal EEG showed marked brainwave slowing and bradycardia during the clinical event. One intra-ictal ICP tracing showed an abrupt and dramatic increase in intracranial pressure during the event. Nineteen patients underwent ventriculoperitoneal shunting and experienced immediate symptom resolution. Anticonvulsant medication, initiated in 11 of these patients prior to shunting, provided no benefit. CONCLUSIONS Plateau wave events are common in patients with NM. They are frequently mistaken for seizures but are easily recognized by a constellation of defining signs and symptoms. Ventriculoperitoneal shunting is curative.