Clinical and Demographic Features of Distal Extremity Weakness in Myasthenia Gravis - A Scoping Review
Authors: Kacar Emrah , Sahadevan Mahavishnu , Leite Maria Isabel 
Published: August 2024

Introduction

Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disease primarily affecting extraocular, bulbar, axial, and proximal extremity muscle groups. However, a subgroup of patients experience distal extremity weakness, known as distal myasthenia gravis (DMG). Despite its longtime observation, DMG’s clinical and demographic features remain poorly understood. This scoping review aims to summarise current evidence regarding the demographic, clinical, and diagnostic features of autoimmune MG patients who exhibit atypical, distal extremity weakness.

Methods

We conducted a scoping review by searching the following electronic databases: Embase, Medline (Ovid), Scopus, Web of Science, and ResearchGate, covering the period from their inception up to August 2024. We included all types of publications due to the limited number of articles available on DMG. Since we wanted to work on individual-level patient data, we selected papers based on our inclusion and exclusion criteria, and interpreted the data descriptively.

Results

After the screening of the initial 2162 publications, we assessed 55 for eligibility. 23 articles (11 case reports, 5 letters to the editor, 2 poster abstracts, and 5 case series) fulfilled the inclusion and exclusion criteria. Demographic and clinical details of 43 patients were extracted for further analysis. The male-to-female ratio was 1.4:1, with a mean (SD) age of MG onset at 40.2 ± 17.2 and a mean age of DMG onset at 44.9 ± 16.3. As 38% DMG patients developed distal extremity weakness at disease onset, in total 55% of DMG patients showed distal symptoms within the first year of their diagnosis. In women with DMG, generalised MG was often present at disease onset (83%), whereas men had similar percentages of ocular (52%) and generalised (48%) MG at disease onset. The most frequently reported weaknesses were in finger extension, followed by wrist extension, elbow extension, and finger abduction. Ankle dorsiflexion weakness was the most frequently reported form of distal lower extremity weakness.

Conclusion

Distal myasthenia gravis (DMG) is a rare yet debilitating subtype of myasthenia gravis. When evaluating MG patients with distal symptoms, it is crucial to consider various differential diagnoses resulting in distal extremity weakness. In this context, we would like to emphasise two MG-associated conditions, namely myasthenia-inflammatory myopathy (MG-IM) and myasthenic neuromyopathy. Our scoping review highlights the need for future prospective studies to address unanswered questions to improve clinical outcomes and the quality of life for patients with DMG.

Highlights

Significant weakness of distal extremity muscles is rare (3-7%) in myasthenia gravis (MG) and is known as distal myasthenia gravis (DMG).

Finger and wrist extensors are the most frequently reported distal muscles affected in DMG.

Approximately 38% of the DMG patients in this review experienced distal extremity weakness at the onset of MG, and a total of 55% developed distal symptoms within the first year of the disease.

At disease onset, 83% of women with DMG presented with generalised MG, whereas men had similar percentages of ocular (52%) and generalised onset (48%).

When evaluating MG patients with distal symptoms, it is crucial to clinically consider two MG-associated conditions, namely myasthenia-inflammatory myopathy (MG-IM) and myasthenic neuromyopathy.