A 59-year-old man comes to the emergency department with diplopia that started several hours ago. His past medical history is significant for long-standing diabetes with poor glycemic control, right-knee osteoarthritis, and peptic ulcer disease. Physical examination shows right-sided ptosis with the right pupil in the inferolateral position. Pupils are equal in size and reactive to light bilaterally. This patient's condition is most likely due to which of the following etiologies?

Question

A 59-year-old man comes to the emergency department with diplopia that started several hours ago.  His past medical history is significant for long-standing diabetes with poor glycemic control, right-knee osteoarthritis, and peptic ulcer disease.  Physical examination shows right-sided ptosis with the right pupil in the inferolateral position.  Pupils are equal in size and reactive to light bilaterally.  This patient's condition is most likely due to which of the following etiologies?

Quizplus · Accepted Answer

11ec160b_39b7_54f1_9249_c5e57939e35a_MD0001_00 Neuropathy is a common chronic complication of diabetes mellitus. The clinical features of diabetic neuropathy vary considerably depending on the pattern of nerve involvement, which can be broadly divided into polyneuropathy, mononeuropathy, and autonomic neuropathy. Mononeuropathies can also be further subdivided into cranial and peripheral types. All ocular motor nerves (III, IV, VI) can be affected in diabetes but unilateral cranial nerve III (CN III) involvement is most common. Diabetic CN III mononeuropathy classically presents with acute onset diplopia. On examination, the affected eye assumes a "down and out" position due to the unopposed pull by the superior oblique (CN IV) and lateral rectus (CN VI) muscles because all other extraocular muscles (inferior oblique and superior, inferior, and medial recti) are supplied by CN III. Ptosis also occurs due to paralysis of the levator palpebrae. Diabetic mononeuropathy is caused by ischemic nerve damage, which predominantly involves the core of the CN III with relative sparing of the peripheral part. The somatic component of CN III that innervates the extraocular muscles is located centrally, but the autonomic component responsible for pupillary constriction and accommodation is located in the peripheral aspect of the nerve. Therefore, pupillary size and reactivity is normal in diabetic CN III mononeuropathy. (Choice A) CN III neuropathy can also occur due to nerve compression. Causes include transtentorial (uncal) herniation, neoplasms, and aneurysms of the posterior cerebral and posterior communicating arteries. In contrast to diabetic CN III mononeuropathy, pupillary dysfunction is often an early manifestation of external nerve compression due to injury of the peripherally located parasympathetic fibers. (Choices B and E) Neither nerve inflammation nor muscle infiltration contributes to the development of diabetic neuropathy. (Choice D) Lacunar midbrain strokes can involve the CN III nuclei. Because many neurologic pathways are densely packed in this area, CN III nuclei impairment is almost always associated with other neurologic deficits (eg, cerebellar ataxia, hemiparesis, or contralateral extrapyramidal symptoms). In addition, the contralateral superior rectus is affected because the subnucleus fibers decussate to the contralateral side. Midbrain lesions also cause bilateral ptosis because both levator palpebrae are innervated by a single subnucleus. Educational objective: Diabetic mononeuropathy often involves cranial nerve III. It is caused by predominantly central ischemia, which affects the somatic nerve fibers but spares peripheral parasympathetic fibers. Symptoms include ptosis, a "down and out" gaze, and normal light and accommodation reflexes. __________ References: Acute ocular motor mononeuropathies: prospective study of the roles of neuroimaging and clinical assessment. (http://www.ncbi.nlm.nih.gov/pubmed/15050435)

A 59-Year-Old Man Comes to the Emergency Department with Diplopia