Question of the Week

A 67-year-old man presents to your glaucoma clinic for his annual exam, accompanied by his wife. He has a history of primary open-angle glaucoma, and you have prescribed latanoprost to achieve a target IOP of less than 18 mmHg. He has a history of Graves' eye disease, for which he is currently taking methimazole. During the exam, he tells you that he recently began experiencing double vision. The symptoms first began about 2 weeks ago, and if he covers one eye, the double vision goes away. His wife also comments that he has looked “tired” recently, and she has noticed his eyelids drooping on several occasions. He denies any muscle weakness. Given this history, you are suspicious of new-onset ocular myasthenia gravis (MG).

Which of the following statements is INCORRECT regarding this situation?

A. Up to 20% of patients who present with isolated ocular MG may progress to generalized MG, but this usually occurs within the first 2 years.
B. The history of thyroid disease should increase your suspicion of myasthenia gravis.
C. You should add timolol to his glaucoma regimen, as it will help lower IOP and reduce symptoms associated with myasthenia gravis.
D. The underlying pathogenesis of myasthenia gravis involves antibodies against acetylcholine receptors.

Answer

The correct answer is C.

Given the patient's history of myasthenia gravis (MG), adding timolol to his treatment regimen should likely be avoided. Timolol, a non-selective beta-blocker, can be absorbed systemically even when used as an eye drop, potentially exacerbating MG symptoms by impairing neuromuscular transmission and increasing muscle weakness. Therefore, in this case, the risk of worsening MG symptoms outweighs the benefits of timolol use. Since MG is an autoimmune disease, other autoimmune diseases can co-occur with MG, and among all autoimmune diseases, autoimmune thyroid diseases are most commonly seen with MG. This is why the history of Graves' disease in this patient should raise concern for a possible overlap with MG, increasing the likelihood of an MG diagnosis (B). It is also true that up to 20% of patients with ocular MG may progress to generalized MG, typically within the first 2 years, which underscores the need for close monitoring of the patient (A). Finally, the underlying pathogenesis of MG involves antibodies against acetylcholine receptors, leading to the hallmark muscle weakness (D).

Amin S, Aung M, Gandhi FR, Pena Escobar JA, Gulraiz A, Malik BH. Myasthenia Gravis and its Association With Thyroid Diseases. Cureus. 2020 Sep 4;12(9):e10248. doi: 10.7759/cureus.10248. PMID: 33042687; PMCID: PMC7536109.