Abstract
Historical reports indicate isolated inferior rectus weakness (IRW) can lead to diagnosis of myasthenia gravis (MG) without additional symptoms. Orthoptists are vigilant to identify IRW, leading to MG investigative testing.
A retrospective consecutive observational case-note analysis of patients who underwent acetylcholine antibody testing (ACR) following presentation to a tertiary adult Strabismus service in Sheffield, 2010-2023, using integrated clinical environment (ICE).
68 patients were identified, 6 were not managed in the strabismus service and excluded (n=62). Mean age at presentation: 60.05 (20-88) years, with 61% male. MG-related signs and symptoms (MG-SS) included muscle weakness, breathing, chewing and swallowing difficulties, slurred speech, variable ptosis/diplopia; variable ocular motility defects, fatigue on elevation, Cogan’s sign. Patients were grouped into isolated IRW (n=10), IRW + MG-SS (n=22), MG-SS without IRW (n=6), thyroid suspected (n=16), suspected MG-related-lids (n=5), suspected MG-related-lids + thyroid (n=3). MG was diagnosed in 10/62 (16.13%), and 6/10 (60%) were ocular MG. 5/10 (50%) IRW + MG-SS, 3/10 (30%) MG-SS without IRW, 2/10 (20%) Thyroid suspected.
The strong predictor for MG is the presence of MG-SS with or without IRW. This highlights the importance to explore MG-SS carefully and not just IRW alone. Other essential assessments should include fatigue on elevation, Cogan’s lids sign and variabilities between assessments.
IRW alone is not a good indicator for MG. It highlights the need to only investigate when MG-SS are present. This will ensure time and cost savings along with reducing psychological impact to patients from unnecessary testing.