Pyrexia & Fever of Unknown Origin Flashcards
how is body temperature controlled
thermoregulatory centre in the hypothalamus (the thermostat)
too hot:
panting, vasodilation, cold seeking behaviour
too cold:
piloerection, shivering, behaviour (curl up)
how does a true fever occur
A variety of stimuli including bacteria, endotoxins, viruses, immune complexes, activated complement, and necrotic tissue trigger the release of endogenous pyrogens by the phagocytic system —> mainly the mononuclear cells or macrophages
These endogenous pyrogens include interleukin-1, tumour necrosis factor (TNF), and interleukin-6
They activate prepotic nucleus of the hypothalamus, raising the set point of the thermostat by generating heat through muscle contraction and shivering, and conserving heat through vasoconstriction
when the hypothalamic set point is increased what is the temp
rarely >41C
what occurs when the hypothalamic set point is increased
body will increase metabolism to adapt to ‘new’ set point
but set point is now variable (alternating cooling and heating)
why are fevers beneficial
Fever enhances WBC activity
- Up to a point
Fever induces acute phase proteins
- Free radical scavenging
Fever decrease viral excretion
- Common cold, chicken pox
what are the costs of fever
Energy
- Fever = increased MER
Physiological processes
- Hemoglobin oxygen dissociation
Collateral damage
WORSE clinical signs
BUT does it matter?
- Ex. You feel better once you take an aspirin
what is hyperthermia
heat generation > heat loss
ex. heat stroke, seizure
is there a set point in hyperthermia
no set point
temp can go >41 when cells will die
what are risk factors do hyperthermia
URT disease
obesity
what occurs during hyperthermia
how is hyperthermia treated and what is contraindicated in these cases
goal is to cool 39.5C in 60-90 mins
do not cool too rapidly
- shivering
- peripheral vasoconstriction
Cool environment
direct cooling
- wet towels
- IVFT
Cardiovascular support
- IVFT
- hypernatremia
- monitor urine output and BP
antibiotics, GI protectants
antipyretics contraindicated
what is the diagnostic approach of FUO
History:
- General history
- Environment (heat stroke)
- In contact animals
Clinical exam:
- Pain?
- Lymph nodes
- ANY mass
- Discharges
what are the causes of acute pyrexia
less than 5 days
mild less than 40.5C
mostly infections (bacterial and viral)
others
- drugs and vaccines
- inflammatory disease
what are the first stages in a diagnosis of FUO
CBC
Serum biochemistry
Urinalysis
Urine bacterial culture and susceptibility
FNA of enlarged organs, masses, or swellings
Second stage:
what are the second stages of diagnosis of FUO
Thoracic radiographs
Abdominal ultrasonography
Echocardiography
Serial bacterial blood culture
Immune tests (antinuclear antibody, rheumatoid factor)
Acute phase reactant measurements (ex CRP)
Serum protein electrophoresis
Serological tests or PCR assay
Arthrocentesis (cytological studies and culture)
Biopsy of any lesion or enlarged organ
Bone marrow aspiration
Cerebrospinal fluid analysis
Leukocyte or ciprofloxacin scanning
Exploratory coeliotomy
what is the third stage of diagnosis of FUO
Therapeutic trial (antipyretics, antibiotics, corticosteroids)
how can antibiotics be used to treat pyrexia
safe relative to NSAIDs/steroids
use first line antibiotics
- Amoxicillin, ampicillin, 1st generation cephalosporins
Avoid TMPS
- Certain dogs can have pyrexic reactions to these drugs
Avoid second line antibiotics if possible
- Fluoroquinolones, cefovecin (convenia)
how can NSAIDs be used to treat pyrexia and when are they use
Direct anti-pyretic effect
- COX-2 inhibition at thermoregulatory centre
Useful if
- Temp >40ºC
- Patient showing adverse effect of fever
- Animal that has been anorexic for 3-5 days
- Obese patients can’t shed heat as easily
- Brachycephalic breeds
- Hot environment
when should you be warely about using NSAIDs to treat pyrexia
Beware of
Patients with renal, GI, liver disease
what are the risks of anti-pyretic therapy
Delays diagnosis
- Proven in small animals!
Side effects of drugs
- Gastric ulceration
- Liver failure
- Renal failure
- Blood dyscrasias
when would corticosteroids be used as anti-pyretic therapy and when should they not be
Same indications as NSAIDs
Maybe more effective
- Immune mediated disease
- Lymphoma (short term only)
But not if the patient has an infection!
- Exclude infectious causes of pyrexia before using corticosteroids
what are the common causes of fever of unknown origin
immune mediated 30-40% (esp steroid responsive meningitis-arteritis (SRMA), immune-mediated polyarthritis (IMPA)
neoplasia 20-30%
infectious 15-20%
other 7-12%
no diagnosis 20%
what are the causes of FUO in cats
Different group of things associated
Feline infectious peritonitis is high on the list compared to inflammatory, neoplastic and more rare immune mediated diseases
what is steroid responsive arteritis-meningitis
Head/neck pain
- Low head carriage
- General depression
- Common in Springer Spaniel
Pyrexia
- Very high
how is SRAM diagnosed
CSF tap
how is SRAM treated
prednisolone
what is immune mediated polyarthritis
Shifting lameness — not necessarily easy to spot
General depression
Pyrexia
Joints may be swollen (not easy to tell)
how is IMPA diagnosed
Diagnosed by joint taps
Do at least 6-8 taps and if all clear can rule it out
Do L+R carpi, stifle and shoulder
Elbows and hocks useful
Visual inspection of joint fluid can be he
what are the signs of endocarditis
Signs
Pyrexia
Joint swelling
Arrhythmias
Murmur
how is endocarditis diagnosed
blood culture
US
how is endocarditis treated
aggressive long term antibacterial therapy
assuming you have no diagnosis for a fever what should you do
Repeat hematology and biochemistry
- Retroviruses, FCoV — cats
- Tick borne diseases — dogs
- Toxoplasma/neospora
- Acute phase proteins
Repeat urinalysis
- Culture (need sterile sample)
- UTI? Pyelonephritis?
Repeat imaging
- Thorax, abdomen and spine
Fine needle aspiration of any mass
- Any mass!
- Normal lymph nodes
Echocardiogram
- Blood cultures
Joint taps
CSF taps
describe a phased approach to a prolonged fever
what are acute phase proteins and what are they useful for
part of innate immune system
measured in 1ml of serum
most sensitive blood test for detecting inflammation
how are acute phase proteins produced
The bacteria and LPS membrane stimulate the production of inflammatory cytokines
These increase the production of proteins that are specifically there to help scavenge products of inflammation
Mop up the bad things that happen during infections
Use them to monitor response
Using the temperature or WBC are too insensitive
