Reversible Dysphagia Due to Gabapentin-Induced Jaw Myoclonus
An 89-year-old woman presented with a 3-day history of dysphagia and lower jaw twitching, which had significantly impaired her ability to drink liquids. The patient had a medical history of hypertension, diabetes mellitus, a surgically corrected left proximal humeral fracture, and right C5 dermatome postherpetic neuralgia. The onset of jaw twitching coincided with her inability to swallow, prompting her admission to the hospital. Physical examination confirmed persistent lower jaw myoclonus, but no other neurological abnormalities were observed. The patient was fully conscious, and there was no evidence of twitching or nystagmus in her extremities. Neurological examination and biochemical analysis, including complete blood profile, electrolyte levels, random glucose concentration, renal function test, and liver function test, were all within normal limits. Computed tomography of the brain revealed no abnormalities, and an electroencephalogram showed no signs of seizure activity.
A thorough review of the patient’s medication history revealed that she had been prescribed gabapentin for allodynia over the right C5 dermatome approximately three months prior. The dosage of gabapentin had been increased to 300 mg total dissolved solids (TDS) two months before her admission. Although her creatinine levels were normal, her glomerular filtration rate (GFR), estimated using the Cockcroft-Gault equation, was 36 mL/min, indicating stage three chronic kidney disease (CKD). Given that the patient’s relatives supervised her medication intake, overdosage was ruled out. Gabapentin was discontinued and replaced with pregabalin 50 mg BD, and the patient was transiently prescribed valium 2 mg TDS. The jaw myoclonus subsided by the second day, and after consultation with a speech therapist, the patient resumed oral intake and tolerated a normal diet. At a one-month follow-up, the patient remained free from jaw myoclonus.
Acute dysphagia in elderly patients is commonly attributed to conditions such as acute stroke and delirium. However, reversible causes like jaw myoclonus are rarely reported. Myoclonus is characterized by sudden, brief, shock-like involuntary movements and can result from various causes, including hypoxic brain injury, metabolic imbalance, focal brain lesions, medications, or viral infections. In this case, the patient scored a six on the Naranjo Adverse Drug Reaction Probability Scale, suggesting that gabapentin was the probable cause of the adverse drug reaction. Literature indicates that 0.1% to 12.5% of patients using gabapentin may experience myoclonus. Gabapentin is primarily cleared by the kidneys, and its half-life can be prolonged to over 20 hours in patients with CKD, compared to 5 to 8 hours in individuals with normal renal function. The patient’s stage three CKD likely contributed to the development of gabapentin-induced toxicity. Notably, the gabapentin dose had been appropriately adjusted according to her CKD, yet it still led to myoclonus. This case represents the second instance where an appropriate dose of gabapentin resulted in myoclonus in a patient with CKD. Previous reports of gabapentin-induced myoclonus typically describe multifocal occurrences, involving asynchronous movements in at least two limbs. Other medications, such as cefepime, have also been associated with jaw myoclonus. Gabapentin-induced myoclonus is generally self-limiting, but in severe cases, low-dose benzodiazepines or renal replacement therapy may be considered.
This case highlights the importance of considering reversible causes of acute dysphagia, including jaw myoclonus, particularly in elderly patients. Clinicians should be aware of the potential for gabapentin to induce jaw myoclonus, especially in patients with CKD. The patient’s symptoms resolved promptly after discontinuation of gabapentin and initiation of alternative therapy, underscoring the need for vigilance in monitoring medication side effects, particularly in vulnerable populations. The case also emphasizes the role of careful medication review and adjustment in patients with renal impairment to prevent adverse drug reactions.
doi.org/10.1097/CM9.0000000000000271
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