Fever and PUO Flashcards
(25 cards)
What is pyrexia of unknown origin?
an illness of more than 2 to 3 weeks of duration with a fever and no diagnosis after intelligent investigations
How much does temperature vary diurnally?
0.5 - 1 degree - highest in the afternoon
Where is temperature regulated?
in the anterior hypothalamus
How does the body lose heat?
peripheral vasodilation, sweating, and reduced physical activity
How does the body conserve heat?
peripheral vasoconstriction, piloerection and warmth seeking behaviour
How does the body produce heat?
shivering, release of thyroid hormones, glucocorticoids and catecholamines
What oral temperature is defined as a fever?
> 37.8
What ear temperature is defined as a fever?
> 38.0
What is the purpose of a fever?
the increase in temperature switches on immune, endocrine and physiological mechanisms for fighting an infection
What is the problem with having a fever for a long time?
it requires a lot of energy so will result in a breakdown of muscle and fat
What is the mechanism of a fever?
bacterial and viral stimuli, Ag-Ab complexes and complement activates monocytes/macrophages and neutrophils and results in release of cytokines (IL-1, IL-6, IFNgamma and TNFalpha) which induces COX-2 to convert arachidonic acid to PGE2 which binds to thermoreceptors in the hypothalamus and stimulates shivering, rigors, vasoconstriction, piloerection, sweating and metabolic changes
Which organisms can directly produce a fever?
gram negative bacteria with an endotoxin in the cell wall
What is rigor?
a feeling of intense cold, uncontrollable shivering, pallor and piloerection - results in a high fever >39
What are some causes of acute fever which are life threatening medical emergencies?
meningococcal septicaemia, falciparum malaria, bacterial meningitis, post splenectomy sepsis, toxic shock syndrome, necrotising soft tissue infections, head and neck space infections, febrile neutropenia, acute staph aureus endocarditis, severe pneumonia
Which patients are more at risk of a life threatening acute fever?
recent OS travel, asplenic, neutropaenia, elderly, diabetic, IV drug users
What is toxic shock syndrome?
where staph aureus or strep pyogenes acts as a super antigen and produces an overwhelming immune response resulting in a rash, hypotension, fever and chills
What associated features make a fever seem more dangerous?
rapid onset, rigors, severe muscle pains, impaired conscious state, vomiting (marker of raised ICP), headache, rash, jaundice
Why do you ask people with a prolonged fever about animal exposure?
because birds can transmit psitacossis which is an atypical pneumonia and Q fever can be transmitted by domestic mammals
Why do you ask people with a prolonged fever about their country of origin?
TB
Why do you ask people with a prolonged fever about travel from a few years ago?
because malaria vivax has a long dormant liver stage
What infection are you worried about in a pregnant mother with a prolonged fever and a young toddler?
CMV
What is the differential diagnosis for a PUO?
infection, connective tissue disorder, malignancy, drug fever, factitious, benign pyrexia
What are the infectious causes of PUO?
subacute bacterial endocarditis, TB, intra abdominal abscess, HIV related opportunistic infection
What are the connective tissue diseases associated with PUO?
polymyalgia rheumatica, temporal arteritis, vasculitis, adult still’s disease, SLE, acute thyroiditis, granulomatous diseases
