120 - Pyrexial illness Flashcards
Why are UTIs common in the elderly?
Low urine flow rate and poor bladder emptying.
Risks of UTIs in patients with diabetes or underlying kidney diseases
Infection can ascend to kidneys from the bladder. Can result in pyelonephritis which can progress to septacemia.
What is pyrexia?
Fever. Common, measurable symptom/sign.
Importance of pyrexia?
Non-specific - generally limited diagnostic significance. BUT Pyrexia of Unknown Origin (PUO) can result in an emergency admission. Need to be able to distinguish between minor and major conditions.
Normal body temp
37.1 degrees Celsius. Can vary between patients.
What is an intermittent fever
Temp returns to normal at least once every 24 hours
Example of an intermittent fever
Malaria
What is a remittent fever?
Fever with peaks/troughs but is always raised and doesn’t return to normal
Example of a remittent fever
Typhoid fever
What is a sustained fever?
Temp stays above normal with only minimal variations. Also called a continuous fever.
Exampled of sustained fever
Pneumonia UTI
What is a recurring fever
Fever with one or more episodes of fever that can last several days with one or more days of normal temperature in between episodes of fever. Also known as relapsing fevers
Examples of recurring fevers
Tick bourne diseases
General rule - relationship between heart rate and temperature
For every 1 degree increase in temp, HR increases by 15bpm
What does the hypothalamus do?
Central to regulation of core body temperature. Acts as a thermostat to control thermoregulatory mechanisms and balance heat loss and heat production
How does the hypothalamus know the body temperature
Heat sensitive receptors in the pre optic area of the hypothalamus is sensitive to increases in blood temperature. Also from the temperature of blood bathing the hypothalamus.
How does the sympathetic nervous system response to an elevated core body temperature?
SNS is inhibited. Vasodilation of blood vessels in skin. Sweat glands stimulated to help loose heat through evaporation. Aiming to reduce temperature back to normal - homeostasis.
What happens when body temp falls below a set point?
SNS is activated. Vasoconstriction of blood vessels in skin. Shivering centre is activated. Sweating is inhibited. Behavioural/endocrine responses to promote heat production are triggered.
Name the 4 successive stages of fever
Prodromal phase Chill phase Flush phase Defervescence phase
What happens in the prodromal stage of fever?
Non-specific complaints Headache, fatigue, general malaise, aching.
What happens in the chill stage of fever?
Feeling chilled and shaking although core body temperature is rising. Shivering stops when temperature reaches new increased set point. Patient tries to get warmer even though temperature is already increased.
What happens in the flush phase of fever?
Vasodilation occurs - skin becomes warm, red and dry.
What happens in the defervescence stage of fever?
Sweating starts
Clinical presentations of fever
Feeling hot Rigors Excessive sweating Headache Delirium Muscle pain Increase respiration rate and heart rate Dehydration
Red flags for sepsis
Severe headache Photophobia
How does temperature normally vary?
Normally tightly controlled. 37.1 degrees Celsius mean with a normal diurnal variation of 0.5 degrees.
How is fever controlled by the body?
Mediated by exogenous and endogenous pyrogens released by cells in response to infection and non-infectious disorders
What is LPS
Lipopolysaccharide. Most studied exogenous pyrogen. Made from broken down cell walls of gram negative bacteria.
What do pyrogens to?
When presented to host cells (e.g. macrophages) - stimulates release of pyrogenic cytokines which act as pro inflammatory stimuli.
Main pyrogen involved in fever and immune responses
Interleukin-6
How do cytokines affect the hypothalamus?
Can cross the blood-brain barrier. Interact with receptors in the pre-optic region of the anterior hypothalamus. Releases prostoglandin E2 which then modifies the responsiveness of thermosensitive neurones.
What drugs can be used to reduce fevers, why?
Antipyretic drugs - NSAIDs, aspirin Affect release of prostaglandin E2 to prevent modification of the thermosensitive neurones in the hypothalamus.
Why do fevers occur in cancer?
Thought to be due to inflammatory cytokines produced either by the cancer or host macrophages responding to the cancer.
What is CRP? Why is it tested for in blood tests?
Acute phase protein that is produced by the liver to help the immune system. Stimulates opsonin to coat bacteria and stimulates recruitment of other immune cells. Marker for infection.
Why is fever thought to be beneficial for the host
Highly conserved, ancient response despite high metabolic costs. IL-1 critical to initiate immune response and is also involved in fever. Small increases in temperature enhances immune function.
What is hyperthermia
Pathological increase in body temperature without a change in set point of the hypothalamic regulatory centre. Caused by excessive environmental heat
Symptoms of heat-stroke
Tachycardia, tachypnoea, BP drops, collapse, seizures. Can be a medical emergency
What is malignant hyperthermia.
Autosomal dominant genetic condition. On exposure to halogenated anaesthetics the body temperature rapidly rises. Can be fatal.
What is neuroleptic malignant hyperthermia?
Psychotropic drugs that block dopamine can cause this in some people. Causes fever, uncontrolled muscle contraction, tachycardia and arrhythmias. Mortality can reach 30%
What is a drug fever?
Fever that starts when a drug is given and goes away when it is stopped. Can be a hypersensitivity reaction so can start weeks after starting the drug.
Define fever
A temperature above the normal range due to an increase in the body’s temperature set point.
Maximum fever
Do not generally of higher than 42 degrees celcius
Treatment for a fever
Generally don’t need to treat a fever on its own but may need to treat an underlying cause. Can treat associated pain and inflammation.
Body temperature control
Ability of an organism to keep its body temperature within certain boundaries even when the environmental temperature is very different
What are pyrogens?
Substance that induces fever. Can be internal (endogenous) or external (exogenous)
Examples of endogenous pyrogens
Cytokines. Produced by activated immune cells and cause the thermal set point of the hypothalamus to increase. IL01, IL-6 are the main cytokines involved.
Examples of exogenous pyrogens
Pathogen factors that act as pyrogens. Key example - Lipopolysaccharide endotoxin found in the cell wall of gram negative bacteria. Immune system triggered by this.
When dealing with pyrexia of unknown origin need to consider:
Infections - TB, Bacterial endocarditis, obscure collections of pus (abdomen, bone). Malignancy Inflammatory disease. Drug hypersensitivity.
What is pyrexia of unknown origin
Fever of >38 degrees that has persisted for at least 3 weeks of illness with no diagnosis despite initial investigations of 3 days as an inpatient or 3 consultations as an outpatient.
How to exclude/monitor pyrexia of unknown origin
3hrly temperature recordings. Consistent with site of taking temperature.
Routine investigations before can say pyrexia of unknown origin
Bloods - FBC, WBC, ESR, CRP Blood culture - 2 minimum 3-6 optimal. Urine, sputum, microscopy. If needed CSF, stool, microscopy Biochem - LFT, U&E, thyroid CXR AFB - if risk of TB
Impact of antibiotics on diagnostic cultures
Reduce usefulness as can modify infection without resulting in a cure.
Impact of corticosteroids when investigating Pyrexia of unknown origin
Reduces usefulness of immunological tests - infection can still progress but masks the inflammation.
Red flags for fever in children
Lethargic, floppy, bulging/depressed fontanelle, non-blanching rash, tachypnoea, tachycardia, vomiting/diarrhoea - can lead to dehydration, poor perfusion (pale, mottled skin), cold hands/feet, leg pain
Fevers in young children are
Common Febrile convulsions - common. Benign rashes - common.
Simple febrile convulsions are
Most common (9/10) Tonic clonic seizures that last
Complex febrile convulsions are
Any seizure with 1 or more of the following features: Lasts >15 mins Symptoms only in 1 part of body Another seizure within 24hrs or during same illness Doesn’t fully recover within 1 hour
What is a risk following complex febrile convulsions
Epilepsy - 1/20 risk.
Elderly patient with no fever can indicate
Dampened immune response. Can indicate poorer prognosis
Most common cause of acute confusion in the elderly
Urinary tract infection - generally E.coli although klebsiella and proteus mirabilis are also common.
Role of mitochondria
Energy production from oxidation of glucose to create ATP
Role of the golgi apparatus
Sorts, packages and modified proteins. Released as vesicles that can merge with plasma membrane to allow secretions.
Role of rough endoplasmic reticulum
Involved in translation and protein folding
Role of smooth endoplasmic reticulum
Involved in synthesis and transport of lipids
Role of ribosomes
Site of translation of RNA into proteins when mRNA meets tRNA
Role of lysosomes
Contain enzymes for cellular digestion
Define infection
Invasion of an organisms tissues by disease causing agents, pathogen multiplication and the reaction produced in the host
Define infectious disease
Illness due to infection
What is Koch’s postulates?
4 criteria that establish a causative relationship between a microbe and a disease. Not always true.
Give the 4 Koch’s postulates
Affects all sick but no healthy people. Can isolate from sick person and culture. Should cause disease if introduced to a healthy organism. Must be recultured from the person it has been introduced into and not have changed.
What are prions
Abnormally folded proteins that cause other proteins to misfold.
What are parasites
Organisms that live in or on another organism and derives nutrients at the expense of the host
What is cellulitis
Superficial infection caused by bacteria. Involves the inner layers of the skin and the subcutaneous fat. Concern if joint involved.
What is erythema?
Redness of skin/mucosal membranes due to increased blood flow in the superficial capillaries.
What are subungual warts?
Warts clustered under the nail. Looks like thickened cauliflower skin around the nail bed.
What are verrucas?
Warts on feet. Flattened as walked on.
What is shingles?
Reactivation of chicken pox. Painful. Rash follows dermatomes and doesn’t cross the midline. Pain first and then rash. Can also develop depression. Treat with acyclovir/other antivirals.
What is eczema herpeticum
Rare but severe disseminated infection that generally occurs at sites of skin damage. Generally caused by herpes simplex virus. Can kill babies.
What is ringworm?
Fungal infection of the skin. Red, scaly, itchy or raised pathech. Patched can be redder on the outside and resemble a ring.
What is lyme disease?
Tick bite from tick infected with Borrelia bacteria results in symptoms including fever, headache, tiredness. Can progress to joint pain, severe headaches, neck stiffness, palpitations and inability to move sides of face if untreated.
What sign is characteristic of Lyme disease?
‘Bulls Eye rash’
Expanding area of redness starting roughly one week after infection has occurred.
25% of patients do NOT get this rash.
