Medial Rectus Nuclear Palsy as a Sole Feature of Midbrain Infarction Secondary to Stenosis of Posterior Cerebral Artery

113 To the Editor: Ophthalmoplegia can cause diplopia, with a lot of etiologies including cerebrovascular disease. Nuclear ophthalmoplegia resulted from brainstem infarction is often accompanied by other symptoms of brainstem dysfunction. It is fairly rare that midbrain infarction only manifests as isolated medial rectus nuclear palsy. Here, we provided such an uncommon case and discussed the possible etiology. A 57‑year‑old right‑handed male patient was admitted to our hospital because of diplopia. Three days ago, he got up with horizontal diplopia which resolved by closing either eye, and he denied other symptoms. On admission, ocular examination only showed left medial rectus palsy, and movement of other extraocular muscles was normal, and pupils were not involved [Figure 1a and 1b]. Other neurological examinations had no positive sign. His past medical history included hypertension for 37 years, and diabetes mellitus for 15 years. He had been a smoker for 30 years with twenty cigarettes per day, and alcoholic for 30 years with 100 ml per day. There were some sporadic old lacunar infarcts affecting both hemispheres on cranial magnetic resonance imaging (MRI) and a fresh ischemic lesion in the right paramedian midbrain on diffusion weighted image [Figure 1c]. To clarify the etiology, head–neck computed tomography angiography (CTA), magnetic resonance angiography (MRA), high‑resolution MRI (HRMRI), ultrasonic cardiogram (UCG), electrocardiogram (ECG) and 12‑lead ECG Holter were completed. The CTA and MRA showed severe stenosis of the proximal segment of the right posterior cerebral artery (PCA) and distal vascular branches reduced [Figure 1d and 1e]. The HRMRI found the atherosclerotic plaque formation in the proximal segment of the right PCA [Figure 1f]. There was no evidence of cardiac construction change on UCG or arrhythmia on ECG. The patient received antiplatelet, lipid‑lowering, antihypertensive, and hypoglycemic treatments. His symptom improved 11 days later at discharge. Isolated unilateral extraocular muscle palsy is usually resulted from lesion in orbit or muscular disease and rarely from cranial nerve or nucleus. In our report, the patient was characterized by right, pure medial rectus nuclear palsy due to acute mesencephalon infarction. To our knowledge, the oculomotor nuclear is situated at the superior colliculus level of the midbrain, which is composed of two parts: the main motor nucleus and the accessory parasympathetic nucleus. The former consists of the lateral somatic cell column, caudal central nucleus, and medial cell column. They innervate superior rectus, inferior rectus, medial rectus and inferior oblique muscle, and levator palpebrae …