Bilateral INO is most suggestive of which of the following conditions?

• A. SLE
• B. Multiple sclerosis
• C. Tuberculosis
• D. Sarcoidosis

Answer: (B)

Bilateral INO arises when the medial longitudinal fasciculus on both sides is damaged, so during horizontal gaze neither eye can adduct effectively and the abducting eye often shows nystagmus. This pattern is most characteristically seen with multiple sclerosis, a demyelinating disease that frequently produces focal lesions in the brainstem including the MLF on both sides, especially in younger adults. While systemic lupus erythematosus, tuberculous meningitis, and neurosarcoidosis can involve the CNS, they do not typically produce the bilateral MLF involvement that creates this distinctive ocular motor pattern, making multiple sclerosis the most likely diagnosis when bilateral INO is observed.