(633) Unraveling Enigma of Syndrome of Irreversible Lithium Effectuated Neurotoxicity: A SILENT Symphony

Introduction: Lithium is the drug of choice for bipolar disorder with the prominent side effect of neurotoxicity. The syndrome of irreversible lithium-effectuated neurotoxicity (SILENT syndrome) is a rare manifestation of neurotoxicity characterized by cerebellar dysfunction with insidious progression in most cases.

Description: A 56 years old lady with a history of hypertension, diabetes, and PTSD was brought to
the emergency due to increased somnolence, one episode of seizure, and no oral intake 2 weeks after her lithium dose had
been increased from 600 mg daily to 900 mg daily. Vitals were normal except for tachycardia of 130 /min. The patient’s Glasgow coma score was 9
(E3V1M4). A neurological exam showed slurred incomprehensible speech, nystagmus, and ataxia. Initial work-up showed elevated lithium (1 mEq/L, therapeutic range 0.8-1.2 mEq/L), and elevated potassium (5.3 mEq/L) which was corrected. A non-contrast CT scan was normal. Lithium was discontinued and intravenous valproic acid and midazolam were started for seizures. The following day, an MRI brain done was normal and an electroencephalogram (EEG) showed a generalized theta slowing with no epileptiform discharges. No further seizure episodes were seen. Lithium levels were monitored and stayed normal over the next 5 days. The patient stayed obtunded with eye-opening and withdrawal to pain.
Subsequent EEGs were normal. However, the patient’s encephalopathy did not improve. SILENT syndrome was suspected and the patient continued to receive supportive management including percutaneous endoscopic gastrotomy (PEG) feeds. After 2 months of lithium cessation, the patient regained complete consciousness and could carry on all activities of daily living independently. The swallowing assessment done was normal and PEG feeds were discontinued.

Discussion: In patients taking lithium, persistent neurological symptoms, particularly cerebellar dysfunction, the
syndrome of irreversible lithium-effectuated neurotoxicity (SILENT) should be suspected even in the
presence of normal lithium levels. The syndrome is rare with an incidence of 0.1 per person per year.
Differentials include neuroleptic malignant syndrome and serotonin syndrome. Management is
supportive with recovery periods ranging from 2 months to 5 years and may need rehabilitation.