Differential Diagnosis for a 79 y.o Male with Nocturnal Fever

Single Most Likely Diagnosis

• Malignancy: Nocturnal fever can be a presenting symptom of various cancers, such as lymphoma. The age of the patient and the specific pattern of fever (occurring only at night and responsive to antipyretics) suggest that an underlying malignancy could be a primary consideration.

Other Likely Diagnoses

• Tuberculosis (TB): TB can cause chronic fever that may worsen at night. Given the patient's age and the nocturnal pattern of fever, TB is a plausible diagnosis, especially if the patient has been exposed to TB or has risk factors such as immunocompromised status.
• Chronic Infections: Chronic infections like endocarditis, osteomyelitis, or abscesses can cause prolonged fevers that may have a nocturnal pattern. These conditions should be considered, especially if there are other symptoms or signs suggestive of infection.
• Autoimmune Disorders: Certain autoimmune diseases, such as rheumatoid arthritis or lupus, can present with fever, although these are less common in the elderly and might not typically follow a strictly nocturnal pattern.

Do Not Miss Diagnoses

• Endocarditis: Although less likely, infective endocarditis is a critical diagnosis not to miss due to its high mortality rate if untreated. Fever is a key symptom, and while it may not always follow a nocturnal pattern, the diagnosis must be considered, especially in patients with valvular heart disease or other risk factors.
• Sepsis: Sepsis can present with fever and is a medical emergency. While sepsis can cause fever at any time, a high index of suspicion is necessary in elderly patients due to their increased risk of severe outcomes.
• Central Nervous System (CNS) Infections: Infections like meningitis or encephalitis can cause fever and must be considered, even though they might not typically cause nocturnal fever exclusively.

Rare Diagnoses

• Familial Mediterranean Fever: This is a rare genetic disorder that causes recurrent episodes of fever, often accompanied by pain in the abdomen, chest, or joints. It's less likely in a 79-year-old without a known family history but could be considered if other diagnoses are ruled out.
• Periodic Fever Syndromes: Other periodic fever syndromes, such as TNF-receptor associated periodic syndrome (TRAPS), are rare and might present with recurrent fevers, although they are more commonly diagnosed in younger individuals.