Misdiagnosis of Third Nerve Palsy

IMPORTANCE: This study identifies the diagnostic errors leading to misdiagnosis of 3(rd) nerve palsy in order to aid clinicians in making this diagnosis. OBJECTIVE: To determine the incidence of misdiagnosis of third cranial nerve palsy (3(rd) nerve palsy) amongst providers referring to a tertiary care neuro-ophthalmology clinic and to characterize diagnostic errors that led to an incorrect diagnosis. DESIGN: Retrospective clinic-based cross-sectional study of office encounters at two institutions from 1/2014 to 1/2017. All encounters with scheduling comments containing variations of “3(rd) nerve palsy” were reviewed. Patients with a documented referral diagnosis of new 3(rd) neve palsy were included in the study. Examination findings including extraocular movement exam, external lid exam, and pupil exam were collected. The final diagnosis was determined by a neuro-ophthalmologist. The Diagnosis Error Evaluation and Research (DEER) taxonomy tool was used to categorize the causes of misdiagnosis. SETTING: Multicenter study describing patients at two neuro-ophthalmology referral centers. PARTICIPANTS: 78 patients referred for a new diagnosis of 3(rd) nerve palsy. MAIN OUTCOMES AND MEASURES: The main outcome measure was the type of diagnostic error that led to incorrect diagnoses using the DEER criteria as determined by two independent reviewers. Secondary outcomes were rates of misdiagnosis, misdiagnosis rate by referring specialty, and examination findings associated with incorrect diagnoses. RESULTS: Out of 78 patients referred with a suspected diagnosis of 3(rd) nerve palsy, 21.8% were determined to have an alternate diagnosis. The most common error in misdiagnosed cases was failure to correctly interpret the physical exam. Ophthalmologists were the most common referring provider for third nerve palsy, and optometrists had the highest overdiagnosis rate of 3(rd) nerve palsy. CONCLUSIONS: Misdiagnosis of 3(rd) nerve palsy was common. Performance and interpretation of the physical exam were the most common factors leading to misdiagnosis of 3(rd) nerve palsy.