Differential Diagnosis for Recurrent Fever in a 74-year-old Male

Single Most Likely Diagnosis

• Chronic Prostatitis: Given the patient's age and recurrent fever, chronic prostatitis is a plausible cause. It can be due to bacterial infection and may not always yield positive blood cultures, especially if the causative organism is not typically found in the bloodstream or if the patient has been partially treated with antibiotics.

Other Likely Diagnoses

• Urinary Tract Infection (UTI): UTIs are common in elderly males and can cause recurrent fever. The infection might not always be detected through blood cultures, especially if it's localized to the urinary tract.
• Pneumonia: Recurrent pneumonia can cause intermittent fevers, and in an elderly patient, the symptoms might be atypical, making diagnosis challenging. Blood cultures might be negative if the pneumonia is viral or if the patient has been on antibiotics.
• Diverticulitis: This condition can cause recurrent fever, especially if there are recurring episodes of diverticulitis or if the condition progresses to a more chronic state. Blood cultures might be negative if the infection is localized.

Do Not Miss Diagnoses

• Endocarditis: Although blood cultures are negative, it's crucial not to miss endocarditis, as it can be life-threatening. Some cases, especially those caused by certain organisms like HACEK bacteria, might have negative blood cultures initially.
• Osteomyelitis: Chronic osteomyelitis can cause recurrent fever and might not always be associated with positive blood cultures, especially if the infection is chronic and localized.
• Abscess: An abscess, particularly in the abdominal or pelvic region, can cause recurrent fever. Blood cultures might be negative if the abscess is not causing bacteremia.

Rare Diagnoses

• Adult-onset Still's Disease: A rare autoimmune condition that can cause recurrent fever, among other symptoms. It's less common but should be considered in the differential diagnosis of recurrent fever of unknown origin.
• Familial Mediterranean Fever: Although more common in certain ethnic groups and typically presenting at a younger age, it could be considered in the differential diagnosis of recurrent fever, especially if there's a relevant family history.
• Relapsing Fever: Caused by Borrelia species, transmitted by ticks or lice. It's rare but can cause recurrent episodes of fever and should be considered based on the patient's exposure history.