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9. Infection (Medical Knowledge) > 4. Pyrexia of Unknown Origin > Flashcards

4. Pyrexia of Unknown Origin Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the normal temperature of humans?

A

37 degrees

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2
Q

What is the definition of a Fever?

A

Elevation of body temperature above normal (37 degrees)

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3
Q

How much can body temperature vary during a fever?

A

0.8 degrees daily
Note - this tends to be with Circadian Rhythm: Low early in the morning, high in the early evening

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4
Q

What is Fever a common and major part of?

A

Systemic Inflammatory Response Syndrome (SIRS)

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5
Q

What is the definition of a Pyrogen?

A

A substance which causes a Fever

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6
Q

What are the 2 types of Pyrogens?

A
  1. Endogenous (e.g. Cytokines)
  2. Exogenous (e.g. Endotoxins from Gram Negative bacteria)
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7
Q

What is the function of Pyrogens, in the body?

A

They act on the Hypothalamic Thermoregulatory Centre to cause reduced heat loss, and hence Fever

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8
Q

What is the Diagnostic Criteria for Pyrexia of Unknown Origin?

A

Temperature of > 38.3 degrees recorded on multiple occasions, which is:
1. Present for at least 3 weeks
2. No diagnosis after 3 outpatient visits
3. No diagnosis after 3 days in hospital
4. No diagnosis after 1 week of outpatient investigation

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9
Q

What are the 4 different types of Pyrexia of Unknown Origin?

A
  1. Classical Pyrexia of Unknown Origin
  2. Nosocomial Pyrexia of Unknown Origin
  3. Neutropenic Pyrexia of Unknown Origin
  4. HIV-Associated Pyrexia of Unknown Origin
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10
Q

What is Nosocomial Pyrexia of Unknown Origin?

A

Pyrexia of Unknown Origin which develops in hospital, and is undiagnosed after 3 days

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11
Q

What is Neutropenic Pyrexia of Unknown Origin?

A

An undiagnosed Fever in a patient which Neutrophils < 500/mm3

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12
Q

What is HIV-Associated Pyrexia of Unknown Origin?

A

Fever in a patient with HIV infection - present and undiagnosed for more than 3 days in an inpatient or 4 weeks in an outpatient

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13
Q

What are the main causes of HIV-Associated Pyrexia of Unknown Origin?

A
  1. Mycobacterium Tuberculosis (21%)
  2. More than 1 causative disease (20%)
  3. Mycobacterium Avium (18%)
  4. Unknown (16%)
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14
Q

What percentage of Classical Pyrexia of Unknown Origin remains undiagnosed?

A

26%

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15
Q

What is the order of the Algorithm to diagnose Pyrexia of Unknown Origin?

A
  1. Complete History and Physical Assessment
  2. Full blood and Urine tests
  3. CT of Abdomen / Pelvis with contrast
  4. Assign most likely category (from History):
  5. a) Infection
  6. b) Malignancies
  7. c) Autoimmune Conditions
  8. d) Miscellaneous
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16
Q

What will the following investigation be, if Tropical Travel is indicated?

A
  1. Bloods for malarial parasites
  2. HIV
  3. Bone Marrow for Leishmaniasis
17
Q

What will the following investigation be, if a New Murmur is indicated?

A

Echocardiography (Tans-Oesophageal may be indicated)

18
Q

What will the following investigation be, if Headaches are indicated?

A
  1. Temporal Artery Biopsy
  2. CT PET
19
Q

What will the following investigation be, if Micro-heamaturia is indicated?

A
  1. Autoantibodies +/- Renal Biopsy
  2. (Polyarteritis) Uktrasound (Renal Ca)
20
Q

What will the following investigation be, if TB contact is indicated?

A
  1. Sputum Smear
  2. Bone Marrow
  3. Mantoux
21
Q

What will the following investigation be, if Drug Misuse is indicated?

A

Screen for blood-borne viruses

22
Q

What imaging techniques are used in Pyrexia of Unknown Origin?

A
  1. CT- PET (most useful)
  2. MRI
  3. Ultrasound
23
Q

What are the disadvantages of imaging in Pyrexia of Unknown Origin?

A
  1. It is hard to do if they have some direction
  2. Cannot always differentiate between infection and inflammation
  3. anatomical changes may not develop in immunocompromised hosts
24
Q

What invasive investigations can be used for Pyrexia of Unknown Origin?

A
  1. Tissue Graft for Culture and Histology
  2. Bone Marrow and Liver are often examined as part of a blind investigation
  3. Diagnostic Laparotomy (Rarely necessary)
25
Q

What is the treatment for Pyrexia of Unknown Origin?

A

Therapeutic Trial (Rarely used) used for:
1. Suspected Mycobacterial infection (unlikely is no response within 2 weeks (use anti-TB therapy))
2. Suspected Vasculitis / Connective-Tissue Disorder (response of Temporal-Arteritis is dramatic (use Steroids))

26
Q

What is a Fabric Fever Pyrexia of Unknown Origin

A

The fever is real but self-induced (like by self-injection)

27
Q

What is the most helpful tool in diagnosing “Fabricated Fever Pyrexia of Unknown Origin”?

A

Microbiology - multiple different organisms on a blood culture
Note - the patient will often continur despite being verry sick, psychiatric expertise should be sought

28
Q

What are the common outcomes of Pyrexia of Unknown Origin?

A
  1. Spontaneous Resolution (commoner in young compared with old)
  2. Some patients respond to NSAID’s / Steroids
  3. Regular Re-appraisal required

9. Infection (Medical Knowledge) (29 decks)

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