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

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.