Differential Diagnosis for Fever and Confusion in Adults

Single Most Likely Diagnosis

• Urinary Tract Infection (UTI): This is a common cause of fever and confusion in adults, especially in the elderly. UTIs can lead to urosepsis, which presents with systemic symptoms including fever, confusion, and altered mental status.

Other Likely Diagnoses

• Pneumonia: Community-acquired pneumonia is a common infection that can cause fever and confusion, particularly in older adults or those with underlying health conditions.
• Sepsis: Sepsis from any source (e.g., bacterial, viral, fungal) can lead to fever and confusion due to the systemic inflammatory response.
• Meningitis: Inflammation of the protective membranes covering the brain and spinal cord, which can be caused by infection (viral, bacterial, or fungal) and presents with fever, headache, stiff neck, and confusion.
• Encephalitis: Inflammation of the brain tissue, most often caused by viral infections, leading to fever, confusion, and altered mental status.

Do Not Miss Diagnoses

• Central Nervous System (CNS) Infections: Including brain abscess, subdural empyema, or epidural abscess, which are less common but potentially life-threatening if not promptly diagnosed and treated.
• Endocarditis: Infective endocarditis, an infection of the heart valves, can present with fever and confusion, especially in intravenous drug users or those with pre-existing heart conditions.
• Neurosyphilis: A complication of untreated syphilis that can cause a range of neurological symptoms, including fever and confusion.
• Cerebral Vasculitis: Inflammation of the blood vessels in the brain, which can lead to fever, confusion, and other neurological symptoms.

Rare Diagnoses

• Prion Diseases: Such as Creutzfeldt-Jakob disease, which are rare, degenerative, and fatal brain disorders that can present with rapidly progressive dementia and confusion, though fever is not typically a primary symptom.
• Whipple's Disease: A rare, systemic bacterial infection that can cause fever, weight loss, diarrhea, and confusion due to CNS involvement.
• Lyme Disease: In its late stages, Lyme disease can cause neurological symptoms, including fever and confusion, though this is less common.
• CNS Lymphoma: A type of cancer that can cause fever, confusion, and other neurological symptoms due to the involvement of the central nervous system.