VCOM Research Day Program Book 2023

Medical Resident Research Case Reports

28 Bulbar-Predominant Presentation of Late-Onset Myasthenia Gravis

Duncan McKinney, MD; Rumana Khan, MD; Edward Griffin, MD Corresponding author: Duncan.mckinney@hcahealthcare.com

LewisGale Medical Center – Salem

Myasthenia Gravis is a relatively uncommon autoimmune condition defined by the production of antibodies which target the post-synaptic receptors of the neuromuscular junction (NMJ). Through this mechanism, the post-synaptic receptors of the NMJ will progressively become more difficult to activate as neurotransmitters, acetylcholine in this case, are blocked from their binding sites by the antibodies and broken down by enzymatic activity. The classical physical manifestation of this disorder is the progressive weakening of muscles, especially with repeated use. MG provides an interesting example of how a single autoimmune condition can result in an array of differing presentations. The majority of patients will notice generalized muscle weakness with a hallmark

finding of ptosis which progresses throughout the day. Atypical cases may instead present with bulbar symptoms such as dysphagia or vocal changes. Aside from the presenting symptoms, MG is also categorized based on the age of onset into early and Late-Onset Myasthenia Gravis (LOMG). This distinction is important as the two groups are known to have differences in the autoantibodies produced and management options. Early-onset MG (EOMG) typically produces the well known acetylcholine receptor (AchR) antibodies as well as DR3 antibodies, while LOMG is less likely to show AchR antibodies and instead have a higher likelihood of producing muscle-specific kinase (MuSK) antibodies. Additionally, it is the EOMG subtype which has a higher frequency of thymoma development. Thymoma resection in EOMG also tends to have

a higher degree of success in terms of symptom resolution when compared to the LOMG/thymoma present counterparts. The consideration and prompt diagnosis of MG, either early or late-onset, is important as these patients are at risk for progression. Should an incorrect diagnosis be made and appropriate management fail to be initiated these patients may progress to myasthenic crisis. The case presented in this article will describe the evaluation, diagnosis and management of LOMG with bulbar-predominant symptoms.

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