Dengue, the second most common vector-borne disease, affects 400 million people annually across 100 countries. Although rare, dengue can cause neurological complications. Despite being considered non-neurotropic, there is growing evidence of direct neuronal infiltration by the dengue virus, as indicated by presence of the virus & anti-dengue IgM antibodies in cerebrospinal fluid. Here, we present a rare case of dengue hemorrhagic fever with encephalitis, emphasizing the need to evaluate dengue infection beyond its typical features.

Dengue encephalitis results from direct viral invasion of the CNS, possibly through a compromised blood-brain barrier. Symptoms include headache, altered consciousness, & seizures, with MRI often revealing involvement of the thalamus, basal ganglia, cerebral cortex, & cerebellar hemispheres. Diagnosis is confirmed by detecting anti-dengue IgM antibodies or dengue genomic material in serum/CSF.

A 27-year-old male presented with high-grade fever, vomiting, & altered consciousness for 2 days. Neurological examination revealed a GCS score of 9/15 (E2+V2+M5). Investigations showed thrombocytopenia & elevated hematocrit, while LFT & electrolytes were normal. Tests for HSV (PCR) & malaria were negative. EEG indicated diffuse seizure activity. CSF analysis showed normal protein & glucose levels, no pleocytosis or oligoclonal bands; however, CSF could not be tested for dengue PCR & IgM antibodies. Serology confirmed presence of dengue PCR & IgM antibodies. MRI showed multiple ill-defined hyperintense areas on T2 & FLAIR in bilateral thalami & hemorrhagic signals in cerebellar hemispheres on SWI, with diffuse mild dural thickening & enhancement over cerebral convexity. After ruling out other viral encephalitides, a diagnosis of dengue hemorrhagic fever with encephalitis was established. The patient received symptomatic & supportive treatment & was discharged after 2 weeks. 

The presentation of dengue viral infection can vary widely, emphasizing the need to evaluate it beyond its typical features. Our case report highlights the importance of considering dengue encephalitis as a differential diagnosis in cases of febrile encephalopathies, especially during a dengue epidemic.