Objective: We aim to raise awareness to an uncommon but possible combination of Parkinson Disease (PD) and Myasthenia Gravis (MG).

Background: The co-occurrence of PD and MG may pose as a challenging diagnosis given the rarity of this combination and the motor impairment seen on both. It is crucial not to miss the diagnosis of MG in a patient with PD since it implies a different treatment approach.

Method: We report a patient with established Parkinson Disease who presented with new-onset generalized weakness and diplopia.

Results: We describe a 76-year-old female, with a previous history of breast and tongue carcinomas treated with surgery and cervical radiotherapy. In 2019 she developed left upper limb rest tremor concomitant with bradykinesia. Brain MRI was unremarkable. The DatSCAN was compatible with bilateral degeneration of dopaminergic neurons of nigostriatal pathways. She was diagnosed with Parkinson Disease (Hoehn&Yahr stage I) and was started on levodopa therapy with good response. In 2023 she complained of generalized fatigue and blurred vision at the end of day. On the neurologic examination she had mild left bradykinesia with no rigidity, bilateral fatigable asymmetric ptosis, immediate vertical diplopia and dysphonia. The patient underwent nerve repetitive stimulation (at 2 Hz and after sustained muscle contraction), which did not show abnormalities but single-fiber electromyography performed on left orbicular oculi muscle revealed  increased jitter in 90% of studied muscle fibers. Accordingly, patient was diagnosed of generalized MG. Chest CT showed no evidence of timoma and the levels of serum anti-nicotinic acetylcbholine receptor (anti-AChR) and anti-muscle specific tyrosine kinase (Anti-Musk) antibodies are pending. She started treatment with pyridostigmine 60 mg 4id and prednisolone 40mg id with the remission of symptomatology.

Conclusion: There is clinical overlap between DP and MG, involving symptoms/signs such as fatigue, motor disability, dysarthria and dysphagia. Our case report reinforces the importance of reconsider the diagnosis when unusual symptoms appear and avoid blaming it on a previously diagnosed entity.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/traveling-through-the-telescope-a-neuromuscular-and-a-movement-disorders-reunion/