[Medial medullary infarction: report of three patients presented with central vestibular dysfunction without limb and lingual weakness].

The purpose of this article is to draw attention to atypical presentation of medial medullary infarction (MMI). With advanced imaging techniques, small infarctions occurring in the medulla are more easily identified. It is difficult, however, to make a clinical diagnosis of MMI if both hypoglossal nerve palsy and limb weakness are absent, because motor weakness is considered a cardinal manifestation of MMI. We describe here three patients who developed central vestibular dysfunction due to MMI without limb and lingual weakness. Case 1: A 44-year-old, diabetic woman developed vomiting and numbness on her left upper limb. Examination revealed unidirectional horizontal and rotatory nystagmus beating toward the right side. There were no Horner syndrome and hypoglossal nerve palsy. Barré arm and leg signs and limb ataxia were absent. Romberg sign was negative. Hypesthesia was present on her left forearm, hand, and fingers. Thumb-localizing test was normal. Cranial MRI demonstrated an infarction in the right paramedian region of the upper medulla. MR angiography demonstrated irregularity of the basilar and the left vertebral arteries. Case 2: A 69-year-old woman suffered from dizziness and nausea. She showed unidirectional, left-beating horizontal nystagmus. There were no Horner syndrome and hypoglossal nerve palsy, Barré arm and leg signs, and limb ataxia. MRI disclosed an infarction in the left upper medial medulla. Case 3: A 47-year-old man developed vertigo when turning over in bed. He showed left-beating nystagmus without latency, when lying down. Horner syndrome and hypoglossal nerve palsy were absent MRI showed bilateral MMI, with the right lesion being larger than the left. MR angiography demonstrated a stenosis in the distal portion of the left internal carotid artery but not in the vertebral and basilar arteries and their branches. This case represents central positional vertigo. Vestibular syndrome seen in cases 1 and 2 was incomplete and incongruent, suggesting dysfunction of the central vestibular system. There have been only nine cases of MMI with horizontal nystagmus in primary position, including unidirectional horizontorotatory nystagmus. In these cases, horizontal nystagmus beats toward the side of the lesion. In sharp contrast, horizontal nystagmus typically beats away from the lesion side in cases of Wallenberg syndrome, suggesting different underlying mechanism. Unidirectional horizontal and rotatory nystagmus is generally associated with peripheral vestibular dysfunction. There has been no reported case of MMI presenting with vestibular dysfunction preserving motor power. Thus, this "benign" form of MMI might have been misdiagnosed as peripheral vestibular dysfunction before the era of MRI.