Lyme disease is endemic to the Northeastern region of the United States. Neuroborreliosis, a term used to describe neurological manifestations of Lyme disease, most commonly presents with radiculitis, cranial nerve palsies, and headache. Rarely, syndrome of inappropriate antidiuretic hormone (SIADH) may also be a clue towards the diagnosis of Lyme disease. 

Cases:

1. 68 year-old male presented with three weeks of progressive left facial droop and weakness of all extremities. Symptoms were preceded by a rash on his abdomen, polyarthralgia, and myalgia. The patient developed hyponatremia 115 during admission. Lyme western blot (WB) was positive for Lyme disease and urine studies indicated SIADH. Subsequent empiric ceftriaxone treatment resulted in a full recovery. 

2. 75 year-old female presented with facial droop, ophthalmoparesis, and an oval rash on her leg. Initial blood work was remarkable for hyponatremia, later deemed to be SIADH per Nephrology team.  Lyme Western Blot testing was indicative of Lyme disease. She completed treatment with doxycycline, which resulted in complete recovery.

3. 77 year-old male presented with painless, horizontal diplopia of ten days duration. On exam, he had CN III, VI, VII palsies. Labs on admission was notable for sodium 126, with urine lytes indicating SIADH. Lyme antibody positive with CSF Lyme WB IgM and serum Lyme WB IgM returned positive.  Completed treatment with 3 weeks of doxycycline.

The association between SIADH and Neuroborreliosis can be important to recognize, raising suspicion for diagnosis of Lyme disease. Early clinical recognition may lead to earlier diagnosis and prompt empiric antibiotic administration, ultimately leading to quicker recovery in these patients.