Fever of unknown origin (FUO)

Question 1

List some DDx for a presentation of:

• 3 week hx fever
• night sweats
• mild abdo pain
• temp 38.5
• nil weight loss

Answer 1

PDx. Fever of unknown origin

1) temp >38.3
2) >3 weeks
3) inconclusive hx, exam, Ix (1st week)

DDx.
Infective:
- TB
- intra-abdo/pelvic abscess (esp diverticulitis, recent surg) 
- HIV
- infective endocarditis
- URTI, LRTI
- UTI
- osteomyelitis
- malaria, typhoid, parasites
Malignancy
- haem: leukaemia, lymphoma, MM
- any primary (esp RCC)
- mets
AI disease
- IBD
- SLE
- RA
- adult-onset Stills disease
- polymyalgia rheumatica 
- giant cell arteritis 
- thyroid (hyperthyroidism, thyroiditis)
- sarcoidosis
Drug induced (B lactam abx, phenytoin, complementary meds)

Question 2

Explain the pathogenesis of fever?

Answer 2

• > trigger:
  1) exogenous: direct stimulation of hypothalamus (e.g. GN toxin)
  2) endogenous (most): immune response -> cytokine release (IL1, IL6, TNFa) -> stimulate hypothalamus indirectly (e.g. tissue damage, infection)
• > act on hypothalamus
• > PEG2 production
• > increase cAMP
• > raise thermoregulatory set point (hypothalamus)

Body response:

• heat conservation: vasoconstriction, piloerection
• heat production: increase basal metabolic rate, shivering

Question 3

List some causative organisms of an intra-abdominal abscess?

Answer 3

Intra-abdo abscess usually due to diverticulosis (colonic mucosal outpouching traps food/faeces -> creates enviro for GIT bacteria to form abscess)
GP:
- staph saprophyticus
- strep
- enterococcus faecalis
GN:
- E. coli (most common)
- klebsiella
- proteus mirrabilis
- serratia
Anaerobes
- bacteroides fragilis

Question 4

How would you treat an intra-abdominal abscess?

Answer 4

Empirical Abx: cover GP, GN, anaerobes

1) Ampicillin: GP cover
2) Gentamicin: GN cover
3) Metronidazole: anaerobe cover