5th June 2025

A 42-year-old female presents to her GP complaining of fatigue, dysphagia and breathlessness.

A 42-year-old female presents to her GP complaining of fatigue, dysphagia and breathlessness. She says she has been newly struggling with daily tasks such as getting up from the chair or combing her hair. She also shows you a new rash on her neck, which she says appeared after going out to the park a few weekends prior when the weather was warm and sunny. She says it is very itchy. On examination, proximal muscle strength is symmetrically reduced 4/5, and distal muscle strength is 5/5. The back of her neck has erythema, with excoriation marks and some blisters. You note bilateral eyelid swelling with some surrounding discolouration.

What is the first-line investigation you should consider? 

Select the SINGLE most appropriate option from the list below. Select ONE option only.