Differential Diagnosis for Intermittent Fevers in Acute Meningitis and Encephalopathy

Single Most Likely Diagnosis

• Viral Meningoencephalitis: This is the most likely diagnosis due to the combination of symptoms such as intermittent fevers, meningitis, and encephalopathy, which are commonly seen in viral infections like herpes simplex encephalitis.

Other Likely Diagnoses

• Bacterial Meningitis: Although less likely than viral causes due to the intermittent nature of the fevers, bacterial meningitis can present with similar symptoms and should be considered, especially if there's a history of exposure or predisposing factors.
• Tick-Borne Illnesses (e.g., Rocky Mountain Spotted Fever, Lyme Disease): These can cause fever, meningitis, and encephalopathy, and their consideration is crucial based on geographical and exposure history.
• Fungal Meningitis: Particularly in immunocompromised patients, fungal infections like cryptococcal meningitis can present with similar symptoms and should be considered in the appropriate clinical context.

Do Not Miss Diagnoses

• Herpes Simplex Encephalitis: Despite being mentioned under the single most likely diagnosis, it's crucial to emphasize its importance here due to its high morbidity and mortality if not promptly treated with antiviral medication.
• Subarachnoid Hemorrhage: Although not typically associated with fever, it can cause sudden onset of symptoms that might mimic encephalopathy and should be ruled out due to its high mortality rate.
• Brain Abscess: Can present with fever, focal neurological signs, and altered mental status, making it a critical diagnosis not to miss due to its potential for severe outcomes if untreated.

Rare Diagnoses

• Autoimmune Encephalitis: Conditions like NMDA receptor encephalitis can present with fever, altered mental status, and seizures, but are less common and might be considered after more typical causes are ruled out.
• Paraneoplastic Syndromes: Rarely, encephalopathy and meningitis can be paraneoplastic manifestations of underlying cancers, and although uncommon, they should be considered in the appropriate clinical context, especially with a history of cancer or unexplained systemic symptoms.
• Prion Diseases: Such as Creutzfeldt-Jakob disease, which can cause rapidly progressive dementia and myoclonus, but are exceedingly rare and typically do not present with intermittent fevers as a primary symptom.