Localizing value of internuclear ophthalmoplegia

Vigneshvarprashanth Umapathy1, Dominic Rodriguez2, Anuvanthana S1, Praneetha A1

1Resident Internal Medicine, Kauvery Hospital, Tennur, Trichy, Tamil Nadu

2Consultant Physician and HOD Internal Medicine, Kauvery Hospital, Tennur, Trichy, Tamil Nadu

Case Presentation

A 66 years aged gentleman who was known to have type 2 diabetes mellitus, systemic hypertension, and residual right hemiparesis following cerebrovascular disease for which he was on low dose aspirin (for 5 years), presented with giddiness, unsteadiness of gait, and visual disturbances for two days.

General examination was unremarkable. His Glasgow coma scale was 15/15. Examination of the central nervous system including the cranial nerves was performed.

When the patient was asked to look to his left, there was a voluntary conjugate deviation of the eyes to the left. However, when he was asked to look to his right, the right eye abducted normally but the left eye failed to adduct and horizontal nystagmus was noted in the right eye when he was asked to look to his right. This clinical finding was suggestive of unilateral internuclear ophthalmoplegia (INO) affecting his left eye (Fig. 1). His pupils were reactive to light bilaterally. He was noted to have residual right hemiparesis. Examination of the other systems was unremarkable.

With a clinical diagnosis of left INO, MRI brain was requested to look for a brainstem lesion in the left paramedian location. MRI brain revealed small focal acute non-haemorrhagic infarct in the posterior midbrain in the left paramedian location (Fig. 2). There was no mass effect or midline shift. Multiple chronic lacunar infarcts in the bilateral basal ganglia, thalamic and corona-radiata regions were also seen.

He was managed medically with dual antiplatelets, atorvastatin, oral antidiabetic drugs and anti-hypertensives.

(a) Baseline, (b) Looking to his left, (c) Looking to his right

Fig (1): Examination findings suggestive of INO of the left eye

Fig. (2): MRI brain revealing small focal acute non-haemorrhagic infarct in the posterior midbrain in the left paramedian location

Discussion

Internuclear ophthalmoplegia (INO) is caused by a lesion in the medial longitudinal fasciculus (MLF). The MLF connects the CN3 nucleus in the midbrain and the CN6 nucleus in the pons on the opposite side and facilitates conjugate eye movements on lateral gaze. In INO, when the patient’s gaze is directed away from the side of the lesion, the ipsilateral (adducting) eye will not adduct and the contralateral (abducting) eye demonstrates horizontal nystagmus.1 Fig. 3 shows the schematic representation of INO affecting the right eye. Fig. 4 represents the volitional saccadic pathway with a right MLF lesion. The aetiologies for INO include: (i) Multiple sclerosis which is often bilateral, (ii) Vascular brainstem lesion which is often unilateral, (iii) Pontine glioma, and (iv) Inflammatory encephalitis affecting the brainstem (autoimmune or infective).1 Myasthenia gravis can mimic INO.

One-and-a-half syndrome, a closely related condition, is a combination of ipsilateral conjugate horizontal gaze palsy (one) and ipsilateral internuclear ophthalmoplegia (a half). This happens when there is an extensive paramedian pontine lesion that involves the MLF and either the CN6 nucleus or the PPRF (parapontine reticular formation). PPRF is the brainstem gaze center that controls the horizontal gaze.1,2

Fig (3): (A) Our patient’s finding (INO of the left eye) compared with (B) schematic representation1 of INO (affecting the right eye)

Fig (4): Volitional saccadic pathway1 with a lesion in the right medial longitudinal fasciculus (MLF) resulting in an INO during an attempted saccade to the patient’s left. (FEF: Frontal eye field)

Learning Points

  • Clinically diagnosed INO leads to accurate localization of lesion in the brainstem.
  • Common causes of INO are:
  1. Vascular: Brainstem – Paramedian posterior midbrain lesion on the side of impaired adduction, often unilateral.
  2. Multiple sclerosis: Demyelination, often bilateral.
  • Pontine glioma
  1. Brainstem encephalitis: Autoimmune or infection
  2. Myasthenia gravis can mimic INO.

References

  • Life In the Fast Lane Blog, Look left, look right, https://litfl.com/look-left-look-right/
  • Xue F, Zhang L, Zhang L, Ying Z, Sha O, Ding Y. One-and-a-half syndrome with its spectrum disorders. Quantitative imaging in medicine and surgery. 2017 Dec;7(6):691.

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