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Medical Student: A rare case of isolated cranial nerve six (CN VI) palsy due to poorly controlled diabetes mellitus
Poster Title: Medical Student: A rare case of isolated cranial nerve six (CN VI) palsy due to poorly controlled diabetes mellitus
Submitted on 28 Oct 2019
Author(s): Christian Freeman MS3; Oguchi Andrew Nwosu MD, FAAFP
Affiliations: Emory University School of Medicine
Poster Views: 275
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Poster Information
Abstract: Case Description: A 58 y/o African American male with PMH of poorly controlled Type 2 DM (A1c 9.6-12.2%) and HTN presented with new onset horizontal diplopia, initially noticed while watching television at home. He was evaluated by Neuro-Ophthalmology and denied any other neurologic symptoms. Ophthalmologic exam at that time was notable for left abduction deficit that was worse on left gaze, concerning for left CN VI palsy. Evaluation revealed no other potential etiology for CN VI dysfunction. Given his vascular risk factors, his symptoms were presumed to be caused by microvascular disease related to his T2DM and/or HTN. He elected the use of an eye patch to mediate his diplopia and subsequently underwent MRI of his orbits which he reports was normal. He continues to follow up with Ophthalmology and his primary care physician to monitor the progression of the visual impairment and maintain adequate control of his diabetes and hypertension.

Discussion/Conclusion: Isolated CN VI palsy has been infrequently reported in patients with DM and/or HTN and is thought to be a manifestation of microvascular disease resulting in thickening and hyalinization of nutrient vessel and subsequent ischemia to the nerve. Though there have been limited prior studies, in instances of isolated CN VI palsy, the prevalence of DM ranges greatly from 4-54% and the prevalence of HTN ranges from 19-71%. One study of isolated CN VI palsy also reported a prevalence of patients with concurrent DM and HTN of 18.4%. Isolated CN VI palsy typically resolves over months to years with proper management of underlying conditions and one observational case series reported recurrence in nearly one-third of patients. Although a rare complication of uncontrolled disease, it is important to consider in patients with otherwise normal neurologic testing in the presence of diplopia.
Summary: Sixth nerve palsy is a rare sequela of microvascular disease related to diabetes mellitus (DM) and/or hypertension (HTN). In the absence of other neurologic signs or symptoms, it is readily distinguishable from other causes of CN VI palsy such as Horner’s syndrome, elevated intracranial pressure, stroke, myasthenia gravis, Giant Cell Arteritis, or thyroid eye disease that would cause limitation of abduction.References: Asbury, Athur K., et al. "Oculomotor palsy in diabetes mellitus: a clinico-pathological study." Brain 93.3 (1970): 555-566.

Patel, Sanjay V., et al. "Incidence, associations, and evaluation of sixth nerve palsy using a population-based method." Ophthalmology 111.2 (2004): 369-375.

Patel, Sanjay V., et al. "Diabetes and hypertension in isolated sixth nerve palsy: a population-based study." Ophthalmology112.5 (2005): 760-763.

Sanders, Scott K., Aki Kawasaki, and Valerie A. Purvin. "Long-term prognosis in patients with vasculopathic sixth nerve palsy." American journal of ophthalmology 134.1 (2002): 81-84.
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