A 17-year-old female presented to the emergency department with a fever of four days duration, frontal and temporal headache, and neck stiffness with no significant medical and drug history. Eight days ago, she had an aphthous ulcer in her mouth, and then maculopapular rashes appeared on her chest. The rashes were painless, without burning or itching, and they disappeared after a day. She had no complaints of vertigo, nausea, and vomiting. She was fully vaccinated, even for corona virus disease 2019 (COVID-19).

On physical examination, she had a heart rate of 130 beats/minute, blood pressure of 120/70 mmHg, and a temperature of 38.6 °C. At the time, no skin lesion or aphthous ulcer was observed. Bilateral cervical lymphadenopathy was noticed without any tenderness or warmness with an approximate diameter of 1.5 cm with a soft consistency. The cardiorespiratory examination was normal, and there was no abdominal organomegaly. Unilateral papilledema (+ 0.5) was observed with fundoscopy in the right eye. Kerning and Brudzinski tests were negative. There was no other lateralized neurological deficit.

Initial laboratory findings revealed the following: white blood cell (WBC) count 6.39 * 103/mm3 (normal value: 4–10.9 * 103/mm3) with 58.5% polymorphonuclear (PMN) and 32.1% lymphocytes, C-reactive protein (CRP) 2.7 mg/l (normal value: 0–6 mg/l), erythrocyte sedimentation rate (ESR) 25 mm/hour (normal value: up to 15 mm/hour), rheumatoid factor 4.3 IU/ml (normal value: up to 20 IU/ml), Wright antigen test 1/20 titer (normal value: less than 1/80 titer), Coombs Wright 1/40 titer (normal value: less than 1/80 titer), Widal antigen test negative, C3 131 mg/dl (normal value: 75–135 mg/dl), C4 31(normal value: 9–36 mg/dl), CH50 90% (normal value: less than 90%), anti-nuclear antibody negative (normal value: up to 1/40 titer), and anti-Smith antibody 0.1 Au/ml (normal value: up to 10 Au/ml). Peripheral blood smear was normal. Serological tests were negative for toxoplasma and Epstein–Barr virus (EBV). Polymerized chain reaction (PCR) was negative for influenza A and COVID-19.

Lumbar puncture was performed on the first day of hospitalization with an opening pressure of 24 mmHg. The CSF analysis showed WBC 30 count/ml (normal value: 0–5 count/ml) (PMN = 70% and lymphocytes = 30%), RBC 80 count/ml, glucose 52 mg/dl (normal value: 50–80 mg/dl) (blood glucose at the same time: 89 mg/dl), and protein 35.5 mg/dl (normal value: 15–40 mg/dl). CSF smear revealed no bacteria in gram stain, and CSF culture was reported negative.

Sonography of cervical chain lymph nodes demonstrated reactive lymph nodes of lateral sides (right 19 mm, left 16 mm). Another oval-shaped reactive lymph node was noticed on the posterior side with a hypoechoic cortex and echogenic fatty hilum (right 21 mm, left 23 mm). Abdominal sonography was normal.

Neurocranium magnetic resonance imaging (MRI) did not show any evidence of encephalitis. Only persistent cavum septum pellucidum and cavum vergae were seen as it is shown in Fig. 1. Electroencephalogram, electrocardiogram, and echocardiography were reported normal.

Persistent cavum septum pellucidum and cavum vergae on brain MRI, coronal, and sagittal views

The result of CSF molecular analysis on day three was positive only for HHV-7. It was negative for all of the following pathogeneses: Neisseria meningitidis, Haemophilus influenzae, Streptococcus pneumonia, Streptococcus agalactiae, Listeria monocytogenes, Cryptococcus neoformans, Treponema pallidum, Mycobacterium tuberculosis complex, Coxiella burnetii, Borrelia burgdorferi, herpes simplex virus 1 (HSV-1), herpes simplex virus 2 (HSV-2), Varicella-Zoster virus (VZV), EBV, cytomegalovirus (CMV), human herpesvirus VI (HHV 6), and human herpesvirus VIII (HHV 8).

The initial treatment included vancomycin, ceftriaxone, and dexamethasone for the first three days. On the third day, based on the positive PCR for HHV-7, acyclovir (500 mg every eight hours) was added to the treatment regimen. On the fourth day, treatment was continued with vancomycin, meropenem, and acyclovir to the end of day nine, and other drugs were discontinued.

The second LP was performed on day four since the fever was persistent. The opening pressure was 20, and fluid analysis revealed: WBC 5 counts/ml (normal value: 0–5 count/ml), RBC 2 counts/ml, glucose 5 mg/dl (normal value: 50–80 mg/dl), and protein 18.4 mg/dl (normal value: 15–40 mg/dl). The CSF molecular analysis was repeated, and it was positive for HHV-7 again.

The headache and fever were discontinued after five and six days respectively. The fundoscopy was repeated on day three which did not show any papilledema. Lymphadenopathy was significantly reduced by day seven. On day ten, the patient had no complaints and was discharged without any further treatment. In follow-up at the clinic one week after being discharged, she remained symptom-free. Lymphadenopathy was fully resolved, and laboratory data were reported normal after one month of follow-up.