Selective or predominant triceps muscle weakness in African-American patients with myasthenia gravis

- The clinical pattern of weakness in MG can be highly variable.
- Selective triceps muscle weakness might be more common in African-American.
- Atypical MG phenotype recognition is critical to avoid unnecessary interventions.

Myasthenia gravis (MG) can lead to weakness in different patterns of muscle groups. Limb muscle weakness is most typically seen in a limb girdle pattern, although variants exist. In the current study, we aimed to describe a unique MG phenotype consisting of selective or predominant triceps muscle weakness. We performed a retrospective review of MG patients who developed focal or predominant triceps muscle weakness between 2006 and 2016. The clinical, electrophysiological and serological characteristics of these patients were examined. 8 MG patients were identified, including 7 males, all of whom were African-American. Two patients underwent muscle biopsy, and one patient underwent cervical spine decompression surgery. All showed significant improvement following immunosuppressive treatment, although one patient experienced a relapse of muscle weakness. This case series highlights a relatively uncommon MG clinical phenotype of selective triceps muscle weakness, mainly in African-American males, in line with previous literature. Familiarity with this phenotype is important in order to facilitate diagnosis and appropriate treatment for this group, and avoid unnecessary investigations or treatments.