To present a diagnostically challenging case of neuroborreliosis with a markedly elevated Lyme Index Value (LIV) but negative confirmatory Western blot. The case illustrates the diagnostic difficulty of neuroborreliosis in the absence of classic peripheral symptoms or known tick exposure.

A middle-aged female presented to the emergency department three times with two weeks of progressive neurological symptoms, including lower back pain, a diffuse burning sensation, right lower extremity weakness, and right-sided paresthesia. She also reported a three-month history of increased fatigue but denied recent illness or known tick exposure.

Initial labs revealed elevated liver enzymes—presumed secondary to acetaminophen overuse for pain—and neutrophilic leukocytosis. Lyme IgM and IgG serologies were positive; however, the Western blot confirmatory test was negative. Notably, the patient had a remote history of Lyme disease and Ehrlichiosis, treated 20 and 10 years ago, respectively.

MRIs of the brain and cervical spine were unrevealing. MRI of the thoracic spine revealed moderate enhancement of the cauda equina, suggesting arachnoiditis, without cord abnormalities. A lumbar puncture demonstrated a lymphocytic pleocytosis (WBC 359) and elevated protein (118 mg/dL), consistent with arachnoiditis. She then completed a 5-day course of high-dose IV corticosteroids.

Subsequently, CSF Lyme Index Value (LIV) returned severely elevated (17; normal <0.7), confirming neuroborreliosis. The patient later developed new symptoms, including vertigo, tinnitus, and headaches, and was treated with IV ceftriaxone and started on gabapentin for symptomatic relief. She remains under close outpatient follow-up.

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