L27: Fever Of Unknown Origin (Harris) Flashcards
Fever of unknown origin
Fever that does NOT resolve spontaneously, doesn’t respond to abx tx, and for which a dx remains uncertain
Initial diagnostic workup for FUO
Hx PE CBC Chem UA urine culture Thoracic and abd rads
Location of thermoregulatory center in CNS
Anterior hypothalamus (AH) -stimulated by peripheral and central thermoreceptors
Mechs. To decrease temp when too hot
Cutaneous vasodilation Panting Postural changes Seeking cool env. Grooming (cats)
Mechs. To increase temp when body too cold:
- cutaneous vasoconstriction
- piloerection
- increased heat production (shiver, inc. catecholamines, inc. thyroxine)
Hyperthermia
Any elevation in core body temp above accepted reference range for that species
-can be pyrogenic or non-pyrogenic
Pyrogenic hyperthermia
(True fever)
-due to an elevation of the thermal set point in the AH 2ary to release of pyrogens
Non-pyrogenic hyperthermia***
Heat gain exceeds heat loss
- inadequate heat dissipation, exercise, pathologic, or pharmacologic causes
- thermoregulatory set point is UNAFFECTED***
Fever is mediated by:
Pyrogens (exogenous and endogenous)
Exogenous pyrogens
- infectious agents
- Immune complexes
- tissue inflammation
- pharmacologic agents (ie. Tetracycline)
**usually INDIRECTLY cause fever by stimulating release of endogenous pyrogens
Endogenous pyrogens
- inflammatory cytokines (released in response to exogenous pyrogens)
- serve to reset thermostat to new higher temp
- cytokines bind to vascular endothelium –> release of prostaglandin E –> thermostat set higher –> body tries to warm itself
Main causes of fever (categories)
1) Inflammatory (infectious)
2) Non-infectious inflammatory
3) immune-mediated
4) neoplastic
5) drug-associated
Most common causes of fever in DOGS**
Infectious
Immune-mediated
Neoplasia
Most common causes of fever in CATS
Infectious
Common cause of fever assoc. with a MURMUR
Endocarditis
Common cause of fever assoc. with the SPINE
Discospondylitis, meningitis
Common cause of fever assoc. with the JOINTS
Polyarthritis
Common cause of fever assoc. with the LONG BONES
Panosteitis, neoplasia, osteomyelitis
Common cause of fever assoc. with MUSCLES
Polymyositis
Common cause of fever assoc. with the PROSTATE
Prostatitis, prostatic dz
Common cause of fever assoc. with the LYMPH NODES
Neoplasia
Infection4
2 main forms of diagnostic approach to a fever**
1) problem-based
2) staged (use if no abnormalities on PE and can’t find problems)
Staging diagnostic approach: stage 1 (least invasive)
- Hx, PE, specialty exams
- CBC, blood smear, Chem with CK
- FeLV/FIV
- UA/urine culture
- thoracic/abd rads
Staging diagnostic approach: stage 2
- repeat stage 1 PRN
- Abd US
- arthrocentesis
- blood cultures
- LN aspirate or other aspirates
- Echo
- long bone/joint rads
- infectious dz titers
Staging diagnostic approach: stage 3 (most invasive/expensive)
- bronchoscopy or BAL
- CSF tap
- dental rads
- bone marrow aspirate
- CT/MRI
- laparoscopy/thoracoscopy
- biopsies PRN
- exploratory sx
- Antinuclear antibody
- Rheumatoid Factor
- coombs test
Changes expected on MDB of fever patient
Systemic inflammatory response:
- inflammatory or stress leukogram
- anemia of chronic inflammatory dz
- mild hypoalbuminemia
- mild hyperglobulinemia
See diagram p. 304**
:)
Why include a CK with chemistry?
Look for evidence of underlying myopathy
Single most important factor for getting a positive blood culture**
Volume of blood taken
-should also collect from multiple sites, preferably during pyrexia
Immune-mediated polyarthritis is a common cause of FUO in dogs even when NO signs of arthritis are present!
Comprise 20-40% of all FUO cases
T/F: a positive serology test automatically confirms infection vs. exposure**
FALSE (ie. With most Lyme, FIP, and toxoplasmosis tests). Likewise, a negative titer does not rule out infection
-a very high Ag result, or seroconversion from negative to positive titers DOES suggest presence of active infection
High IgM antibody levels against an organism occur when?
During early exposure
Guidelines for therapeutic trial if a diagnosis for fever can’t be made:
1) begin with tentative diagnosis (and avoid therapies that limit what you can do in the future)
2) treat with appropriate dose and duration
3) define parameters
4) consider coincidental response (have a way to measure response)
Risks for therapeutic trial
- continued progression of dz
- medication side effects/toxicities
- exacerbate underlying infectious dz if immunosuppressive tx used
At what temp does fever become life threatening?
> 106
Why is artificial cooling not indicated in pyrogenic hyperthermia cases?
- thermostat already set higher, so you just end up making body work harder against being cooled
- only helpful if have non-pyrogenic hyperthermia
When is tx with antipyretic therapy (NSAIDs) indicated for hyperthermia?
- uncommonly, since doesn’t tx underlying dz
- when we have a dx for an underlying cause but there is no specific treatment for it
- causes transient improvement of CS
MOA of NSAIDs
-inhibit COX pathway of the arachidonic acid cascade therefore decreasing prostaglandin synthesis
Best way to address fever without interfering with many diagnostics
Fluid therapy
Should NOT have a fever with a simple cystitis*
:)
