Fever of unknown origin causes

Resident Survival Guide

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Naresh Mullaguri, M.B.B.S. [2]

Synonyms and keywords: febris continua e causa ignota; febris e causa ignota; febris E.C.I.; FUO; PUO; pyrexia of unknown origin

Overview

Classic FUO may be caused by infection, neoplasia, inflammatory , miscellaneous diseases, and undiagnosed illness.Common causes of neutropenic FUO include bacterial, fungal and viral infection.Causes of nosocomial FUO are related to hospital setting such as drugs, infections acquired during hospitalization and complications that occur during and after surgery.This may due to acute infection from HIV itself earlier or later due to opportunistic bacterial, fungal and viral infections such as mycobacteria, toxoplasma etc.

Causes

Etiology is different for different categories of FUO:

Classic FUO

1. Malignancies such as Hodgkin and non-Hodgkin lymphoma, myeloproliferative disorders, colorectal carcinoma and carcinoma of liver.
2. Infections such as intrabdominal and pelvic abscesses, inflammation of the endocardium, tuberculosis, cat scratch disease, CMV and EBV infections.
3. Inflammatory causes such as autoimmune diseases (systemic lupus erythematosus, Rheumatoid arthritis) and polymyalgia rheumatica.

Neutropenic FUO

These are mostly caused by bacterial, fungal and viral infection because of the decreased neutrophil count.

HIV associated FUO

This may due to acute infection from HIV itself earlier or later due to opportunistic bacterial, fungal and viral infections such as mycobacteria, toxoplasma etc.

Nosocomial FUO

Causes of nosocomial FUO are related to hospital setting such as drugs, infections acquired during hospitalization and complications that occur during and after surgery.