Isolated Abducens Nerve Palsy in an Adolescent With Confounding Multisystem Serology: A Case Report and Diagnostic Review

Cranial nerve palsies in pediatric patients are rare and can be challenging to diagnose due to the broad spectrum of potential causes, including infections, inflammation, neoplasms, and idiopathic conditions. Abducens nerve palsy (ANP), though uncommon, is of particular interest due to its association with both intracranial and systemic pathologies. We present the case of a 16-year-old male who developed isolated left ANP of presumed infectious-inflammatory origin. Initial neurological and ophthalmological assessments revealed esotropia and marked abduction deficit without other cranial nerve involvement. Brain magnetic resonance imaging showed enhancement of the left abducens nerve consistent with neuritis, while cerebrospinal fluid analysis and initial laboratory investigations were unremarkable. Serological testing revealed low-positive IgM for <i>Mycoplasma pneumoniae</i>, <i>Chlamydia pneumoniae</i>, Herpes simplex virus (HSV)-1/2, and <i>Borrelia burgdorferi</i>, while polymerase chain reaction for HSV and Borrelia were negative. The patient was treated with corticosteroids, antibiotics, and antivirals, showing mild improvement in eye mobility, and follow-up imaging revealed resolution of the inflammatory changes. Despite persistent low IgM positivity in subsequent tests, the patient fully recovered within 6 months. Although the exact etiology remains unclear, the combination of clinical response and serological findings suggests a possible infectious or immune-mediated process. This case underscores the diagnostic complexity of pediatric ANP and highlights the importance of considering a broad differential diagnosis and using a multidisciplinary approach in management. Further research is needed to better understand the role of mild serological findings and improve diagnostic strategies for such conditions.