BackgroundHeadache and Neurologic Deficits with cerebrospinal fluid Lymphocytosis (HaNDL) is a rare and underdiagnosed syndrome that mimics recurrent stroke, migraine with aura, and encephalitis.ObjectiveDescribe the presentation, clinical characteristics, and cerebrospinal fluid (CSF) findings in a patient with HaNDL and provide insight into the importance of the recognition of this syndrome.MethodsThe authors describe a unique case of (HaNDL) during which the patient underwent three lumbar punctures over 26 days.ResultsThe authors demonstrate the natural course of CSF characteristics of a patient with HaNDL, with rising and falling lymphocyte counts. Additionally, the authors provide an example of the clinical presentation of HaNDL, with episodic attacks over the course of 1 month of migraine headache, hemibody paresthesias, hemibody weakness, and encephalopathy.ConclusionsHaNDL is a headache syndrome mimicking viral encephalitis, migraine with aura, and recurrent cerebral ischemic events. While HaNDL is a diagnosis of exclusion, the syndrome's association with characteristic clinical and laboratory findings are important to recognize. Furthermore, a monophasic pattern of CSF lymphocytosis in HaNDL may be observed.Implications for NursingIncreased recognition of this syndrome may help prevent unnecessary tests and treatments when patients present with recurrent episodes.