Medicine JC095: Fever Flashcards

1
Q

Normal body temperature

A

Varies at different site of measurement:
- Oral: 33.2-38.2 (vary with food intake)
- Rectal (most resemblance to core body temp): 34.4-37.8 (less variation)
- Tympanic: 35.4-37.8
- Axillary: 35.5-37.0 (less variation)
—> peripheral temperature need to do adjustment: ∵ affected by circulation (e.g. vasoconstriction, hypotension, shock —> not necessarily mean patient has hypothermia)

Normal temperature also depends on:
1. Age (elderly has lower normal temperature ∵ lower metabolic rate)
2. ***Sex (female: ↑ after ovulation)
3. Time of measurement (↓ in midnight, ↑ in afternoon —> +/- 0.5oC from mean temp)
4. Activity level
Etc.

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2
Q

Physiology of Temperature regulation

A

2 main components:
1. **Hypothalamus (Temperature regulating centre: Thermostat)
2. **
Peripheral regulatory mechanism
—> Very important to distinguish between Fever vs Hyperthermia

↑ Body temp
—> detected by Thermostat
—> ↓ Heat production + ↑ Cooling effect + Voluntary response

↓ Heat production:
- ↓ SNS —> ↓ Basal metabolic rate

↑ Cooling effect:
- ↓ SNS —> Vasodilation
- ↑ PNS —> Sweating

Voluntary response:
- ↓ Activity
- Exposing body to cold environment
- Cold drinks
- Loose clothing

↓ Body temp
—> detected by Thermostat
—> ↑ Heat production + ↓ Cooling effect + Voluntary response

↑ Heat production:
- ↑ Thyroid hormone —> ↑ Basal metabolic rate
- ↑ SNS —> ↑ Basal metabolic rate
- Shivering

↓ Cooling effect:
- ↑ SNS —> Vasoconstriction
- ↑ SNS —> Piloerection

Voluntary response:
- ↑ Muscle activity
- Seek heat source
- Eat
- Warm clothing

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3
Q

***Mechanism of Fever

A

Definition of Fever:
- Thermostat reset at Hypothalamus

LPS from Gram -ve bacteria / Infections
—> Monocyte activation
—> **
Pyrogenic cytokines (
IL1, TNFα, IL6)
—> Stimulate *Endothelium of Hypothalamus (
LPS can also directly stimulate it)
—> ***PGE2 production (main mediator to adjust thermostat)
—> Neurotransmitter, cAMP
—> ↑ Set point in Hypothalamus
—> Peripheral heat response (↑ Heat production, ↓ Cooling effect)
—> Fever (result of readjusting set point in Hypothalamus)

End result:
1. Vasoconstriction —> Chills
2. Shivering —> Rigor (not necessarily depend on how high the thermostat adjusted, if little elevation of set point —> other mechanism enough to generate enough heat)
—> above usually occur ***before onset of fever (high body temperature)

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4
Q

Definition of Fever

A

Oral: 37.8
Rectal: 38
Tympanic: 38
Axillary: 37.2

Hyper-pyrexia:
- ***Core temperature (NOT peripheral) >40
- indicate serious underlying condition
- may lead to permanent brain damage

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5
Q

***Fever patterns

A

Varies with different causes of Fever
- NOT 100% sensitive / specific

  1. Continuous fever:
    - Temp NOT fluctuate >1oC
    - Causes: ***Pyrogenic infections, Dengue fever, Fungal infections
  2. Remittent fever:
    - Temp **remains above normal + fluctuate >1oC
    - Causes: **
    IE, Brucellosis, Typhoid fever
  3. Intermittent fever:
    - Elevation of temp only present for a certain period (e.g. 1-2 hours), in between body temp is **normal
    - Causes: **
    Malaria, TB, Lyme disease, Borreliosis, EBV
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6
Q

***Fever vs Hyperthermia

A

Fever:
- **Change in Hypothalamic set point
- Heat production / Cooling mechanisms intact (e.g. cool limbs during fever)
- Involves **
Pyrogenic cytokines (IL1, TNFα, IL6, IFN)
- Diurnal variation usually ***preserved

Hyperthermia:
- **Failure in thermoregulation (imbalance between heat production / cooling mechanisms) (e.g. unable to sweat during exercise if severe dehydration)
- Thermostat / Hypothalamic set point is **
normal
- Diurnal variation lost
- e.g. **Heatstroke, Malignant neuroleptic syndrome, Serotonin syndrome, **Thyroid storm

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7
Q

***Causes of Fever

A

Infections:
- Virus
- Bacteria
- Fungus
- Parasite

Autoimmune disease (activate monocytes / pyrogenic cytokine production):
- SLE
- Sarcoidosis
- Adult Still’s disease
- Giant cell arteritis

Malignancies:
- Lymphoma
- Leukaemia
- RCC (most classic example of ***solid organ tumour causing fever)

Tissue destruction:
- Massive infarction
- Massive haemolysis
- Rhabdomyolysis

Metabolic disorders:
- Gout
- Porphyria

Drugs:
- Antibiotics
- Anticonvulsants (technically cause hyperthermia due to SE to thermoregulation / muscle contraction)

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8
Q

***Pyrexia of unknown origin

A

Old definition (vague):
- Fever **>38.3 on several occasions
- Duration **
>3 weeks
- Unable to reach a diagnosis despite ***1 week of inpatient investigation

Current definition (more widely accepted):
- Prolonged fever without an obvious identifiable cause

Proportion of fever:
- PUO > CT disease > Infection > Malignancies > Miscellaneous

Rmb:
- Most fever that persist beyond a period are caused by common conditions presenting **uncommonly
- Many conditions can cause PUO
- **
Infection a significant cause (∵ ↑ global travel + use of immunomodulating drugs e.g. immunosuppressants, chemotherapy) —> need to **exclude Infection first!
- Most PUO in developed world caused by **
Non-infectious inflammatory disorders (malignancy a much smaller percentage)
- PUO DDx depend on:
—> time
—> regional factors
—> exposures
—> available diagnostic tools
- Significant % of PUO are caused by miscellaneous conditions
- ***No standard algorithm for evaluating PUO

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9
Q

***Etiologies of PUO

A

Infection:
- **Endocarditis (need echo) > **Mycobacterial (esp. extrapulmonary) > Abdominal abscess (now easier to diagnose by advances in imaging)

Malignancies:
- ***Lymphoma > Solid organ tumour

Autoimmune diseases:
1. **SLE
2. **
Systemic vasculitis
3. ***Adult Still’s disease
(- RA, Psoriatic arthritis, Spondyloarthritis usually not present with high fever —> low grade fever only)

Drug fever:
1. **Hypersensitivity reaction (∵ pyrogenic cytokine production)
- **
Type 3 (Immune complex-mediated (Ag-Ab complex) —> Complement activation —> Attract Neutrophil —> Cytokines) (e.g. Serum sickness syndrome by drug —> GN, Arthritis, Rash, Fever)
2. Altered thermoregulatory mechanisms
3. Reactions that are direct extensions of pharmacological action of drug
4. Other Idiosyncratic reaction

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10
Q

Drug fever: 2. Altered thermoregulatory mechanisms

A
  1. Exogenous ***thyroid hormone
  2. Drugs with ***Anticholinergic activities (∵ ↓ sweating, urinary retention)
  3. ***Sympathomimetic agents (∵ ↑ SNS, e.g. recreational drugs: ecstasy, amphetamine —> agitation, twitching, cold extremities due to vasoconstriction, ↑ HR, mydriasis, sweating but less prominent than heat production mechanisms)

Differentiating Anticholinergic vs Sympathomimetics:
- Dry skin vs Sweaty skin

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11
Q

Drug fever: 4. Idiosyncratic reactions

A

Idiosyncratic: not based on primary pharmacological effect of medications, SE unpredictable

  1. **Malignant hyperthermia (esp. after **antipsychotic)
  2. ***Neuroleptic malignant syndrome
  3. Serotonin syndrome (SSRI, ***Tramadol)
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12
Q

***Diagnostic approach to PUO

A

History
1. Localising symptoms (e.g. chills, rigor)
2. **Intake of drugs (drugs that cause fever, drugs that alter immunity)
3. Travel
4. Animal exposure
5. **
Risk of immunosuppression

P/E
1. **Organomegaly (malignancy)
2. CT disease
- Rash
- Arthritis
- Vasculitis
—> **
small vessels (e.g. **ANCA-associated vasculitis —> Renal involvement: Proteinuria, Haematuria; Lung involvement)
—> **
large vessels (e.g. **Temporal arteritis in elderly, **Takayasu’s arteritis)

Laboratory tests
1. ESR
- RBC stacked together (Rouleaux: one of major determinants of ESR)
—> promoted by **APR, **Ig (↑ during acute inflammation)
—> decreased by **Albumin (↓ during acute inflammation)
- less specific: also ↑ by ↑ age, female sex
- **
↑: infection, TB, multiple myeloma, hypergammaglobulinaemia, pregnancy, anaemia, renal disease, ↑ age, female sex (RBC stick together —> sink more rapidly)
- ↓: RBC abnormalities, extreme leukocytosis, hyperviscosity (i.e. a lot of other components prevent sinking of RBC)

  1. CRP
    - IL6, IL1β —> ↑ CRP synthesis by ***liver
    - false negative: IL6, IL1β blockers
  2. **Procalcitonin
    - Calcitonin: ONLY produced by Thyroid C-cells normally
    - Procalcitonin: during **
    Bacterial infection
    —> Bacterial infection —> IL1β, TNFα, LPS —> ↑ gene transcription of Procalcitonin in **ALL organs
    (—> Viral infection —> IFNγ —> ↓ gene transcription of Procalcitonin)
    - Rise and drops significantly **
    within 3 days —> also helpful to monitor treatment response

Imaging
1. CT
2. MRI
3. Gallium scan
4. ***PET-CT (more specific than Gallium scan)

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