Introduction: Third (3rd) nerve palsy is characterized by some combination of ptosis, limited adduction, supraduction, infraduction, and pupillary function. Causes include microvascular ischemia, compression, and aneurysms. Accurate diagnosis is essential to avoid potentially life-threatening consequences and unnecessary testing. We assessed the frequency of 3rd nerve palsy misdiagnosis based upon referrals to two high volume tertiary care neuro-ophthalmology services, and characterized the specific diagnostic errors.

Methods: A retrospective review of patients with 3rd nerve palsy was identified by searching for variations of “3rd nerve palsy” in scheduling comments for referrals and final diagnosis of “3rd nerve palsy”. Patients were excluded from the review if they lacked adequate referral documentation or had a known history of compressive brain mass or aneurysm. Incorrect referral diagnoses were analyzed using the DEER criteria.

Results: 69 patients were reviewed with 44 meeting inclusion criteria. Among the cohort referred for 3rd nerve palsy, 24% were found to have alternate diagnoses including myasthenia gravis, thyroid ophthalmopathy, congenital strabismus, and internuclear ophthalmoplegia. Among subjects with final diagnosis of 3rd nerve palsy, 25% were referred for diagnoses including myasthenia gravis, vision loss, and unspecified diplopia. The most common reason identified for misdiagnosis was misinterpretation of exam findings. Failure in hypothesis generation, inadequate physical exam, and failure to weigh clinical history were also common reasons for misdiagnosis.

Conclusions: Misdiagnosis of 3rd nerve palsy was common in referrals to two tertiary neuro-ophthalmology centers. Careful attention to physical exam and a focused differential diagnosis are key factors in correct diagnosis of 3rd nerve palsy.

Patient Care: By identifying and reducing the unnecessary misdiagnosis and referrals for third nerve palsy, a substantial amount of time and resources can be diverted towards more adequate medical problems.

Learning Objectives: By the conclusion of this session, participants should be able to identify the prevalence of third nerve palsy misdiagnoses and the most common reasons why.

References: Graber, Franklin, Gordon., Diagnostic Error in Internal Medicine. Arch Intern Med,165:1493-9, 2005 Norman, Young, Brooks. Non-analytical models of clinical reasoning: the role of experience. Medical Education 2007: 41: 1140–1145, 2006 Eva, Cunnington, The difficulty with experience: does practice increase susceptibility to premature closure?, J Contin Educ Health Prof, 26:192–8, 2006 Voytovich, Rippey, Suffredini, Premature conclusions in diagnostic reasoning, J Med Educ, Apr;60(4):302-7, 1985 Crosskerry, The Importance of Cognitive Errors in Diagnosis and Strategies to Minimize Them, Acad. Med, 78:775–780, 2003 Trobe, Searching for brain aneurysm in third cranial nerve palsy. J Neurophthalmol, 29:171-173, 2009