In this article we will discuss about the Pyrexia of Unknown Origin (PUO):- 1. Causes of PUO 2. Infection of PUO 3. Laboratory Diagnosis.
Causes of PUO:
The most common causes of prolonged PUO are:
(a) Chronic infections;
(b) Tumours,
(c) Connective tissue disorders;
(d) Granulomatous diseases
(e) Drug hypersensitivity reactions (Table 94.1):
Infection of PUO:
Aetiology:
As a cause of PUO, infections account for about 35% cases. Without accurate determination of the nature and location of infection, many cases of PUO due to infecting agents, agents are eradicated by blind anti-microbial therapy.
(a) Bacterial Infections:
Due to repeated blood culture and widespread use of antibiotics, bacterial endocarditis due to streptococci is a sure cause of PUO; but antibiotic use or infection by highly fastidious organisms, fungi (Candida, Aspergillus), Rickettsiae and Bacteroides are important factors in culture-negative endocarditis.
Certain organisms (S. typhi, S. choleraesuis), Neisseria meningitidis and Brucella give rise to chronic intermittent bacteriaemia without prominent localised findings.
Sinusitis, mastoiditis, sub-acute osteomyelitis (particularly vertebral osteomyelitis), retroperitoneal abscesses and secondarily infected organised clot of an aortic aneurysm also present as PUO. Gram-negative bacilli (E. coli, Bacteroides and Salmonella have been recovered from these patients. In such patients, blood culture usually becomes intermittently positive.
Viral Infections:
(1) Infections mononucleosis due to Epstein-Barr virus.
(2) Cytomegalovirus infection
(3) Hepatitis A
Infected patient with these viral infection may suffer from prolonged febrile illness without prominent localised findings.
(C) Parasitic Infection:
(1) Protozoal diseases Malaria, amoebic hepatitis or liver abscess, visceral leishmaniasis (Kala-azar), toxoplasmosis, and trypanosomiasis.
(2) Metazoal Disease:
Filariasis, particularly during first year of infection.
Laboratory Diagnosis of PUO:
A. Hematology Rarely specific.
B. Biochemistry
Liver function tests reveal liver damage in relevant cases.
C. Bacteriology:
1. Blood culture-should be done
2. Anaerobic culture of pus
3. Mycobacterial culture
4. Urine culture.
D. Serology:
Useful in infections mononucleosis (Paul Bunnel test) enteric fever, hepatitis A, B infection, lyme disease, CMV infections and sometimes in amoebiasis.
5. Skin Test:
Mantoux test for histoplasmosis, coccidioidomycosis, sarcoidosis (Kvelm-Siltz- bach skin test).
6. Other Tests:
(i) Immunologic tests (LE cells phenomenon, antinuclear antibody test in SLE etc.).
(ii) Biopsy of lymph node or other tissues.