Case Report: Abducens Nerve Palsy Could Be Sign of Myasthenia Gravis

Myasthenia gravis (MG) often begins with ocular symptoms, and sometimes those symptoms remain isolated to the eyes. However, a new case report shows how symptoms of ocular MG (OMG) can vary, and on rare occasions appear as isolated abducens nerve palsy.

This new report was published in Cureus.¹

The case involved a 68-year-old male patient who told clinicians he woke up one morning with double vision in his right eye and photophobia, explained the study authors. The patient had a history of aortic stenosis and hypertension, along with insomnia and prostate cancer. His active prescriptions included a nasal spray for allergies and eszopiclone (Lunesta; Waylis Therapeutics) for insomnia, both taken as needed.

The patient was referred to ophthalmology, where he was diagnosed with sixth cranial nerve (abducens) palsy and referred for an MRI of the head and CT angiogram of the head and neck, the authors said. The MRI showed cerebellar tonsillar ectopia, but no intracranial abnormalities; the CT angiogram findings were unremarkable.

The patient who was the subject of this case report had a history of aortic stenosis and hypertension, along with insomnia and prostate cancer | Image Credit: Alessandro Grandini-stock.adobe.com

The patient was next referred for a neuro-ophthalmology appointment, where clinicians noted a deficit in his right lateral rectus muscle, as well as increasing esotropia on right gaze and dermatochalasis in both eyes. Those findings led the patient’s physicians to suspect OMG, and they proceeded to measure his acetylcholine receptor (AChR) antibodies for confirmation. Those tests were positive for AChR binding antibody (1.86 nmol/L; reference interval: 0.00-0.24 nmol/L) and AchR blocking antibody (35%; reference interval, 0%-25%).

“Based on the positive AchR antibodies in addition to isolated ocular manifestations, the patient was diagnosed with OMG,” the authors wrote. “Moreover, a follow-up visit with outpatient neurology established no evidence of generalized MG (GMG) based on unremarkable findings in the physical examination.”

The patient was prescribed 60 mg of pyridostigmine (Mestinon; Bausch Health Companies), to be taken 3 times daily. After 2 months, the patient said his vision had improved, although physicians noted continued medial deviation in the right eye. The patient will be monitored to see if symptoms worsen, the authors said.

They highlighted that the patient in this case was typical in some regards. Men are more likely to be diagnosed with MG at an older age, they said, and ocular symptoms are often the first signs of MG. OMG also predominantly affects male patients, they added.

However, patients with OMG typically present with ptosis and diplopia, the authors said, whereas this patient’s case presented with symptoms of isolated cranial nerve palsy.

“To our knowledge, there are limited studies or case reports that explore the prevalence of the different isolated cranial nerve palsies in patients with MG,” they said.

One exception, however, is a 2009 study that analyzed 49 patients with OMG. That study found that just 6 cases mimicked isolated cranial nerve palsy.² Only 4 patients presented with isolated abducens nerve palsy.

Despite its rarity among patients with OMG, the present study authors said abducens nerve palsy is the most common cranial nerve neuropathy among people in this patient’s age group (60-70 years). They noted that the nerve issue is often caused by diabetes or hypertension, but can also be associated with trauma or tumors.

“As OMG can mimic these cranial nerve palsies, it is important to first rule out strokes and tumors in patients who present with cranial nerve palsies,” the authors wrote. “However, in the case that strokes and tumors are negative, clinicians should have a high suspicion for OMG and include it in their list of differential diagnoses.”

They closed by stating that their case not only shows the importance of considering OMG but also the importance of a thorough medical history and clinical assessment in order to identify patients like this with OMG.

References

1. Sanchez JC, Belmar MT, Sanchez J, Mercen JL, Prieto J. A male patient presents with isolated abducens nerve palsy: an atypical presentation of ocular myasthenia gravis. Cureus. 2024;16(4):e57501. Published 2024 Apr 3. doi:10.7759/cureus.57501

2. Cleary M, Williams GJ, Metcalfe RA. The pattern of extra-ocular muscle involvement in ocular myasthenia. Strabismus. 2008;16(1):11-18. doi:10.1080/15569520701830992