Lyme Neuroborreliosis Presenting As Diplopia and Syndrome of Inappropriate Antidiuretic Hormone Secretion

Lyme neuroborreliosis represents the neurologic manifestations of disseminated Lyme disease, typically presenting as meningitis, cranial neuropathy, or radiculoneuropathy. Although syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a recognized complication of central nervous system infections, it is not commonly associated with Lyme neuroborreliosis, and only a few linked cases have been reported in the literature. This case describes a male in his 50s who presented to the emergency department with severe headache, diplopia with inability to abduct the right eye, back pain, and hyponatremia secondary to SIADH. Initial neuroimaging revealed optic neuritis, and CSF analysis revealed lymphocytic pleocytosis, elevated protein, and an increased total nucleated cell count. Oligoclonal bands were also detected in the CSF. While multiple sclerosis was initially clinically suspected, Lyme disease screening via enzyme-linked immunosorbent assay (ELISA) was performed because of the patient's location in the Northeastern United States and returned positive. Subsequent confirmatory Western blot analysis was positive for IgG and negative for IgM. The patient was treated with IV ceftriaxone followed by a 21-day course of doxycycline, after which his neurologic symptoms, headache, and hyponatremia resolved.