Incidence and clinical characteristics of concurrent thyroid eye disease and ocular myasthenia gravis.

OBJECTIVE

To examine the incidence and clinical characteristics of concurrent thyroid eye disease (TED) and myasthenia gravis (MG) and identify potential diagnostic clues for this rare coexistence.

METHODS

A retrospective observational study included 15 patients diagnosed with both TED and MG between May 2013 and July 2025. The diagnosis of TED was based on Bartley's criteria, and MG was diagnosed using criteria from the Japanese Ministry of Health, Labour, and Welfare. Clinical data, including ocular alignment, eyelid position, thyroid function, antibody profiles, imaging findings, treatment, and outcomes, were reviewed.

RESULTS

Of 6 576 TED patients, 15 (0.23%) were diagnosed with concurrent MG, and 12 (0.18%) had isolated ocular MG (OMG). Ptosis was observed in 9 patients (60.0%), and vertical strabismus was the most common pattern (53.3%). Exotropia, an unusual presentation in TED, was seen in 6 patients (40.0%). Extraocular muscle inflammation was confirmed on magnetic resonance images in 11 patients (73.3%). Steroid pulse therapy, administered to 8 patients (53.3%) for active TED, also improved MG symptoms. At a mean follow-up of 43.8 ± 36.6 months, 10 patients (66.7%) showed significant improvement in ptosis and/or diplopia.

CONCLUSIONS

Concurrent TED and MG, while rare, present overlapping features that can complicate diagnosis. Atypical signs, such as ptosis with diurnal variability and exotropia with vertical misalignment in TED patients, should raise suspicion for MG.