Worsening of Myasthenia Gravis following the Addition of Gabapentin for Essential Tremor

Objective: To report a case of worsening myasthenia gravis after the initiation of gabapentin for treatment of essential tremor. Case Summary: A 69-year-old man experienced minor ptosis of the left eyelid, slight neck weakness, and transient difficulties in chewing food on day 6 of a slow gabapentin dosage titration. As the titration continued, the myasthenia symptoms progressed to bilateral ptosis, and there was dramatic worsening of weakness by day 23. He was taking gabapentin 1500 mg daily at the time; the drug was then tapered to discontinuation. All myasthenia gravis symptoms were reported as resolved 3 days after discontinuation of gabapentin. The initiation and discontinuation of gabapentin also coincided with improvement, then worsening of the patient's tremor. Discussion: Three published case reports describe worsening of myasthenia gravis during use of gabapentin for the treatment of various neuropathies. To the best of our knowledge, this is the first case report of a patient experiencing worsening of myasthenia gravis upon initiation of gabapentin for essential tremor. The Naranjo probability scale suggests a probable association between gabapentin and worsening of myasthenia gravis symptoms in our patient. Several myasthenia-like symptoms are listed in the gabapentin mongraph as low-frequency adverse events, increasing the possibility that gabapentin may have been unmasking or worsening myasthenia gravis in clinical trials. However, myasthenia gravis is not identified as a contraindication or caution for gabapentin use. Conclusions: Gabapentin should be used with caution in patients with myasthenia gravis, and clinicians must be aware of the potential risks of this therapy.