Differential Diagnosis for New-Onset Confusion and Associated Symptoms in an Older Adult Patient

The patient presents with new-onset confusion, change in vision, headaches, nausea, photophobia, and vital signs indicating a fever and tachycardia. Given these symptoms, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Meningitis: This is the most likely diagnosis given the acute onset of confusion, fever, headache, nausea, and photophobia. These symptoms are classic for meningitis, an inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. The presence of fever and altered mental status, in particular, points towards an infectious process like meningitis.

• Other Likely Diagnoses

  • Hypertensive Encephalopathy: Although less likely given the presence of fever, hypertensive encephalopathy could explain the confusion, headaches, and visual changes if the patient's blood pressure were significantly elevated. However, the blood pressure provided (122/79) does not support this diagnosis as the primary cause.
  • Alcohol Withdrawal: Given the patient's history of alcohol use disorder, alcohol withdrawal could be considered, especially if the patient has recently reduced or stopped alcohol intake. Symptoms can include confusion, tremors, seizures, and hallucinations, but typically do not include fever or photophobia as prominent features.

• Do Not Miss Diagnoses

  • Subarachnoid Hemorrhage: Although less likely given the absence of a reported "thunderclap" headache, subarachnoid hemorrhage is a critical diagnosis not to miss due to its high morbidity and mortality. It can present with sudden headache, confusion, and sometimes fever if there is associated meningismus.
  • Encephalitis: An inflammation of the brain tissue, usually caused by viral infections. Symptoms can include fever, confusion, headache, and sometimes seizures or focal neurological deficits. It's crucial to consider encephalitis due to its potential for severe outcomes if not promptly treated.
  • Septic Encephalopathy: In the context of fever and confusion, considering an underlying sepsis causing encephalopathy is crucial. This condition can arise from any severe infection and leads to brain dysfunction.

• Rare Diagnoses

  • Posterior Reversible Encephalopathy Syndrome (PRES): A rare condition associated with high blood pressure, eclampsia, and certain medications. It can cause headaches, confusion, seizures, and visual disturbances. However, the blood pressure in this case is not significantly elevated, making this less likely.
  • Wernicke's Encephalopathy: A neurological disorder caused by thiamine (vitamin B1) deficiency, often seen in patients with alcohol use disorder. It presents with confusion, ataxia, and ophthalmoplegia. While important to consider in this patient population, the presence of fever and photophobia is not typical for Wernicke's encephalopathy.