Myoclonus Secondary to Baclofen Toxicity in the Setting of End-Stage Renal Disease on Hemodialysis: A Case Report

Case Diagnosis: Myoclonus Secondary to Baclofen Toxicity in the Setting of End-Stage Renal Disease on Hemodialysis

Case Description or Program Description: 53-year-old male with end-stage renal disease on hemodialysis, recurrent right basal ganglia intracerebral hemorrhage, atrial fibrillation not currently on anticoagulation, known bilateral carotid stenosis, presented to the emergency department due to altered mental status (AMS), right upper extremity rhythmic-clonic movements, and aphasia. At baseline, the patient is awake, alert, oriented, and has dense left-sided hemiplegia (face, arm, leg) with residual dysarthria. The patient was started on baclofen 5 mg twice daily per outpatient neurology for spastic hemiplegia six days prior to presentation. CT head, CTA head/neck, MRI brain no contrast, and EEG were negative. Consulted for aphasia, Physical Medicine & Rehabilitation (PM&R) immediately provided recommendations to hold baclofen. On exam, the patient also had hyperreflexia and left ankle clonus. Of note, nursing at bedside said that patient missed two hemodialysis sessions before admission. At the time of evaluation, the patient was receiving hemodialysis.

Setting: Acute inpatient hospital

Assessment/Results: The patient’s mental status improved significantly the next day after completing hemodialysis, treating hypoglycemia, and discontinuing baclofen, gabapentin, and mirtazapine. By discharge, the patient underwent two more hemodialysis sessions and returned to baseline mental status with resolution of myoclonus. AMS was thought to be in the setting of hypoglycemia and baclofen use with possible contributions from gabapentin and mirtazapine.

Discussion (relevance): Hypotonia, hyporeflexia, and flaccidity are consistent with baclofen toxicity, while hypertonia, hyperreflexia, and spasticity are symptoms in withdrawal. However, this patient had myoclonus, which is an atypical presentation of baclofen toxicity.

Conclusions: The exact baclofen dose threshold over which toxicity occurs is unclear, especially in patients with severely reduced kidney function. Renally-cleared medications like baclofen should be titrated cautiously to avoid toxicity, which may need to be differentiated from potential withdrawal. PM&R consults can play a significant role in identifying such conditions.