P48 A case of myasthenia gravis presenting to the rheumatology clinic
Authors: Yeoh Su-Ann , Salam Sharfaraz , Christofi Gerry , Morris Vanessa 
Published: April 2020

Abstract

Background
A 32-year-old Lithuanian lady, with a 6-year history of undifferentiated inflammatory arthritis and autoimmune neutropenia, contacted her rheumatologist reporting a constellation of new symptoms. This began with a month’s history of facial weakness and slurred speech. She progressively experienced nasal regurgitation on drinking fluids, reduced exercise tolerance, as well as difficulty chewing, swallowing, and coughing. Her symptoms initially came on in the evening but subsequently appeared earlier in the day. There were no symptoms suggestive of infection. Her arthritis had been well-controlled on hydroxychloroquine and sulfasalazine. She was previously on methotrexate, but this was discontinued due to plans to conceive.

Methods
Clinical examination during an urgent outpatient review yielded dysphonic, mildly dysarthric speech. Extraocular movements were normal with no ophthalmoplegia. There was mild lower motor neurone facial weakness and an absent gag reflex. She demonstrated fatiguability on repetitive tongue movements and arm abduction. There were no upper motor neurone or cerebellar signs. Blood tests showed normal inflammatory markers, full blood count, creatine kinase, immunoglobulins, liver, and renal profile. Her anti-nuclear antibody titre, previously weakly positive at time of diagnosis of inflammatory arthritis, was 1:1280 (homogenous). Anti-cyclic citrullinated peptide, rheumatoid factor, and extractable nuclear antigens were negative. Virology screen was unremarkable. Neurology input was sought. Anti-acetylcholine receptor antibody was positive at 5.2nmol/L (normal range 0-0.45nmol/L), anti-muscle specific receptor tyrosine kinase antibody was negative. Nerve conduction studies showed decremental response on repetitive stimulation of her left nasalis, consistent with a post-synaptic neuromuscular junction transmission disorder. There was no evidence of myopathy.

Results
The clinical symptoms and the investigations led to the diagnosis of myasthenia gravis with predominant bulbar features. Computed tomography showed no evidence of thymoma or thymic hyperplasia. Magnetic resonance imaging of the brain showed no evidence of space-occupying lesion or brainstem abnormality. She initially received pyridostigmine 30mg three times daily with propantheline cover to which she reported a good response. A viral illness led to deterioration of her symptoms of breathlessness and worsening dysphagia resulting in a hospital admission. She received intravenous immunoglobulins 20g daily for three days. Hydroxychloroquine and sulfasalazine were replaced with methotrexate 15mg weekly. She now remains on pyridostigmine 90mg five times daily and 10mg prednisolone daily with good effect.

Conclusion
Myasthenia gravis is a rare condition (prevalence of 10-20 per 100,000 in the United Kingdom). However, this occurs at a higher prevalence in autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. This case illustrates the importance of remaining vigilant about symptoms which patients may disclose in the rheumatology clinic which may not fit with their known diagnosis. Her previous use of methotrexate for her arthritis could have masked her myasthenic symptoms which became apparent after the drug was stopped for a prolonged period.

Disclosures
S. Yeoh None. S. Salam None. G. Christofi None. V. Morris None.