Working Diagnosis:
Congenital cranial nerve 4 palsy

Treatment:
Corrective lenses and protective eyewear were recommended.

Outcome:
In the setting of sport-related facial trauma, the patient was provisionally cleared for sport after evaluation by an eye doctor.

Author's Comments:
While nearly 50% of trochlear nerve palsies are congenital (1) their prevalence has not been described in athletes let alone considerations for participation in sport. Most of the literature in athletes addresses traumatic etiologies(2). Moreover, our case highlights several PPE principles. First, the PPE aims to promote safe participation and not to restrict physical activity: 14% of athletes require further workup and 98% are cleared (3). While there are no validated screenings in athletes (4), a general exam should be performed followed by focused evaluations based on abnormal histories and exam findings. Our athlete's diplopia and gaze deficit prompted a full neurologic exam. The provider should have a low threshold to involve a specialist to help determine eligibility, which in our case was Ophthalmology. Lastly, decisions around clearance are best made using a shared decision-making model.

Editor's Comments:
Trochlear nerve palsy is the most common cause of acquired vertical diplopia due to paralysis of the superior oblique muscle, leading to weakness of downward movement of the eye. In the prior population-based case-series, the annual incidence was estimated to be 5.73 per 100,000 per year with the most common cause being presumed congenital, followed by trauma and hypertension. The patient with trochlear nerve palsy often presents with a characteristic head tilt, approximately 70% of all patients, where the patient tilts their head away from the affected side. Though rare, approximately 3% of patients can present with a head tilt toward the injured side, known as the paradoxic head tilt. Though it likely was not present in this athlete, these compensations can signal clinicians to have a closer look with a potential referral during PPE or sideline coverage.

Additionally, the author brings up several important points regarding the principles of preparticipation examination. This case highlights the importance of thorough history taking and physical examination and an individualized approach using a shared decision-making model when determining medical eligibility for athletes to participate in sports safely.

References:
1. Khanam S, Sood G. Trochlear Nerve Palsy. [Updated 2024 Sep 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK565850/
2. Stiller-Ostrowski JL. Fourth cranial nerve palsy in a collegiate lacrosse player: a case report. J Athl Train. 2010 Jul-Aug;45(4):407-10. doi: 10.4085/1062-6050-45.4.407. PMID: 20617917; PMCID: PMC2902036.
3. Smith J, Laskowski ER. The preparticipation physical examination: Mayo Clinic experience with 2,739 examinations. Mayo Clin Proc. 1998;73(5):419-429. doi:10.1016/S0025-6196(11)63723-3
4. Bahr R. Why screening tests to predict injury do not work-and probably never will...: a critical review. Br J Sports Med. 2016;50(13):776-780. doi:10.1136/bjsports-2016-096256

Acknowledgments:
N/A

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