Isolated atrophy of the abductor digiti quinti in patients with rheumatoid arthritis

We aim to discuss the association of isolated atrophy of the abductor digiti quinti muscle in patients with rheumatoid arthritis as well as review the anatomy and imaging findings of this condition on MRI.

A consecutive series of 55 patients diagnosed with rheumatoid arthritis according to the 2010 ACR/EULAR classification criteria were recruited. MRI of the clinically dominant feet was performed using a 1.5-T scanner.

The study population was predominantly female (94.5%), and the age range was 31-79 years (mean 57.5 ± 11). A total of 55 ankles were examined by MRI, and 20 patients (36.3%), all females, showed abductor digiti quinti denervation signs. Seven patients demonstrated severe fatty atrophy of the abductor digiti quinti, corresponding to Goutallier grade 4, 2 patients showed moderate fatty atrophy (Goutallier grade 3), and the remaining 11 patients showed less than 50% fatty atrophy, corresponding to a Goutallier grade 2. Substantial agreement was found for both intra- and interobserver agreement regarding the Goutallier grading system.

Prevalence of signs of abductor digiti quinti denervation on MRI was high in the studied population, suggesting that rheumatoid arthritis may be associated with inferior calcaneal nerve compression.