Erdheim-Chester disease is a rare non-Langerhans cell histiocytosis (LCH) that affects different body systems. It was recently recognized as a neoplastic disorder after identifying an activating mutation of the MAPK pathway. Neurological presentations of ECD are rare. We present a case of a 35-year-old male who presented to the emergency department with neck pain, headache and vomiting for 2 months; MRI showed multiple heterogeneous intracranial masses. Neurosurgery performed a suboccipital craniotomy, partially resected the cerebellar mass, and placed a parietal to frontal shunt catheter. Biopsy results from the cerebellar mass demonstrated cerebellar tissue involved by a diffuse proliferation of foamy histiocytes and spindle cells admixed with prominent lymphoplasmacytic infiltrate and positive for CD68, CD163, Factor XIIIa and Fascin. PET scan showed hypermetabolic uptake within the medullary portions of the diffuse abnormal lesions of the distal femurs, tibias, and fibulas, and cardiac MRI was nonsignificant. The patient was started on vemurafenib and continued to show improvement in a 3-month outpatient follow-up.

Human herpesvirus-6 (HHV-6) is a virus known for causing the highly contagious infection, roseola infantum, and has been associated with causing encephalitis in pediatric patients and less commonly in adult patients as well. Regardless of the patient's age, the primary HHV-6 infection could be complicated by neurological sequelae including encephalitis, acute encephalopathy with biphasic seizures syndrome, or demyelinating disease. HHV-6 encephalitis does occur in an adult as a primary infection or reactivation. However, immunocompromised, hematopoietic stem cell transplantation patients, and solid organ transplant recipients are the most affected population. Here we present a rare case of HHV-6 encephalitis in a 26-year-old healthy immunocompetent male. HHV-6 viral DNA was detected in the cerebrospinal fluid during the acute stage of the disease, and the diagnosis was confirmed by quantitative polymerase chain reaction (PCR). The patient was treated with ganciclovir and had a complete response to treatment without any further complication. The pathophysiology, clinical course, and treatment in otherwise immunocompetent adult patients are also discussed.

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