A previously healthy 16-year-old boy from Eastern Ontario presented with a 2-day history of tactile fever, left-sided weakness and confusion. He was amnestic of an event from the previous day consisting of driving a tractor into a ditch, during which no head or other trauma was sustained. Six days prior, he began having headaches, vomiting, diarrhea and cough. He had a tick bite 1 week prior and a recent nasal herpetic flare. There was no additional history of trauma, ingestion or travel. Immunizations were up to date. On examination, he was somnolent, febrile and able to follow 2-step but not 3-step commands and showed signs of slow processing and poor working memory. His speech was hypophonic and mildly dysarthric, but cranial nerve examination was otherwise normal. There was paratonia of the right arm, mild spasticity of the left arm and normal tone in the legs. Strength was mildly decreased in the left upper and lower extremity proximally and markedly decreased in the distal upper extremity. Reflexes were brisk in the upper extremities, slightly brisker on the left and normal in the lower extremities. Plantar responses were flexor. Sensation was intact.
Complete blood count and electrolyte concentrations were unremarkable, and blood culture was negative. Cerebrospinal fluid (CSF) analysis demonstrated an elevated white blood cell count of 124 × 106/L (80% lymphocytes, 2% neutrophils and 18% mononuclear cells), elevated protein of 0.79 g/L and normal glucose of 3.2 mmol/L. Magnetic resonance imaging of the brain showed T2 hyperintensities and loss of gray–white matter differentiation in bilateral mesial temporal lobes and hippocampi (worse on the right) and subtle abnormalities in the bilateral superior frontal gyri (Fig. 1), suspicious for herpes simplex virus (HSV) encephalitis. Electroencephalogram also showed intermittent generalized slowing especially on the right. Intravenous acyclovir and ceftriaxone were initiated on admission. CSF polymerase chain reactions (PCRs) for HSV and enterovirus were negative, and thereafter intravenous immunoglobulins (IVIg) and pulse corticosteroids were given for possible autoimmune encephalitis. Ceftriaxone was discontinued after bacterial cultures returned negative at 72 hours, but acyclovir was continued because of ongoing concern of HSV encephalitis.
Given a lack of clinical improvement after 5 days, a repeat lumbar puncture was performed, showing a CSF white blood cell count of 79 × 106/L (94% lymphocytes, 1% neutrophils, and 5% mononuclear cells). HSV PCR was repeated on this sample, and again was negative. Serologic testing was negative for antibodies to anti-N-methyl D-aspartate receptor, cytomegalovirus, Epstein-Barr virus, varicella zoster virus and human immunodeficiency virus. Serum was also sent for another test, which ultimately revealed the diagnosis.