Extrinsic allergic alveolitis

Disease class: lung diseases, Interstitial

Also known as

• Hypersensitivity pneumonitis

[Immunology] Introduction

Immunologists specialise in diseases of the immune system, including allergies. The spleen and bone marrow are closely associated with immunological diseases.
There is significant overlap with rheumatology, haematology, and medical genetics.
This is a pathology discipline.  

 

Etymology

Latin immūnis, immūnis, immūne = exempt, immune
Ancient Greek λογία (logia) = study

Immunology = the study of immunity (resistance against infectious diseases)

 

Subspecialties

• Allergy medicine / allergology

 

Investigations

 

History taking

 

Physical examination

 

Key presenting complaints, reasons for referral

• Allergic reactions (type 1 hypersensitivity)  
• Angioedema
• Anaphylaxis 
• Allergic contact dermatitis (type 4 hypersensitivity) 
• Frequent infections
• Rare or severe infections 

Immune system diseases 

Relevant diseases

• Atopy
• Asthma
• Allergic conjunctivitis 
• Atopic dermatitis (eczema)
• Allergic rhinitis (hay fever)
• Drug allergy
• Food allergy  
• Urticaria (hives) 
• Hypersensitivity
• Eosinophilic granulomatosis with polyangiitis 
• Granulomatosis with polyangiitis
• Hereditary angioedema
• Primary antibody deficiencies
• Hypogammaglobulinaemia
• Primary immunodeficiency disorders
• Autosomal recessive hyper-IgE syndrome
• X-linked Severe combined immunodeficiency (SCID)
• Wiskott-Aldrich syndrome
• Secondary immunodeficiency disorders

Angioedema

Disease class: Vascular diseases

Bronchial hyperreactivity

Disease class: Bronchial diseases

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Biochemistry homepage  

 

Clinical indications:

 

Profile:

 

Specimen type: 

 

Sample type: 

 

Turnaround time: 

 

Acute severe asthma

Also known as status asthmaticus.
This is a medical emergency caused by an abrupt and severe attack of asthma. 

 

Assessment of severity

Moderate acute asthma

• Increasing symptoms
• Peak flow > 50-75% best or predicted
• No features of acute severe asthma

Severe acute asthma
Any one of the following:

• Peak flow 33-50% best or predicted
• Respiratory rate ≥ 25/min
• Heart rate ≥ 110/min
• Inability to complete sentences in one breath

Life-threatening acute asthma
Any one of the following, in a patient with severe asthma:

• Peak flow < 33% best or predicted
• Arterial oxygen saturation (SpO₂) < 92%
• Partial arterial pressure of oxygen (PaO₂) < 8 kPa
• Normal partial arterial pressure of carbon dioxide (PaCO₂) (4.6–6.0 kPa) (type 1 respiratory failure)
• Silent chest
• Cyanosis
• Poor respiratory effort
• Arrhythmia
• Exhaustion
• Altered conscious level
• Hypotension

Near-fatal acute asthma

• Raised PaCO₂ (type 2 respiratory failure)
• Requiring mechanical ventilation 
• Requiring mechanical ventilation with raised inflation pressures

 

Management

• Airway management
• Tracheal intubation
• Mechanical ventilation

Allergic rhinitis

Disease class: Rhinitis

Also known as hay fever. 
This is an atopic disease.

It can progress to sinusitis.

Management

• Oral anti-histamines
• Anti-histamine nasal spray 
• Corticosteroid nasal spray
• Anti-histamine eye drops

Hypersensitivity

Disease class: Immune system diseases

Hypersensitivity refers to pathology caused by excessive immune system activity.

Types 

• Type I: Immediate hypersensitivity or allergy
• Type II: Antibody-mediated disorders
• Type III: Immune complex–mediated disorders
• Type IV: T cell–mediated hypersensitivity or delayed type hypersensitivity
• Type V: Receptor-mediated autoimmune diseases

Urticaria

Also known as hives or allergic urticaria.

Caused by a type 1 hypersensitivity reaction. Associated with atopy.

Causes rapid-onset pruritus (itchiness) and erythema (redness).

Managed with anti-histamines.

Type I hypersensitivity

Hypersensitivity

Also known as immediate hypersensitivity or allergy

 

Examples 

• Allergic rhinitis 
• Allergic sinusitis
• Anaphylaxis
• Asthma 
• Atopy
• Eosinophilic granulomatosis with polyangiitis (Churg-Strauss Syndrome)  
• Food allergies

Mechanism

1. Immunoglobulin E (IgE) molecules bind to an antigen called an allergen. 
2. IgE molecules on the surface of mast cells and basophils become cross-linked by allergens. 
3. Mast cells and basophils degranulate, releasing various vasodilators such as histamine and inflammatory mediators such as prostaglandins. 
4. Local blood vessels dilate and become more permeable. 
5. Fluid leaves the circulation into the tissue spaces. The tissues swell.

Anaphylactic shock

Also known as anaphylaxis.

This is a type of distributive shock caused by an allergic (type 1 hypersensitivity) reaction. Huge amounts of fluid leave the vasculature and enter tissues spaces throughout the body.

There is a significant reduction in the volume of blood circulating around the cardiovascular system. The blood pressure falls and and the pulse rate will often increase to compensate.

In distributive shock, fluid is lost from the circulatory system, but it remains inside the body.

Causes

• Common food allergens
• Prescribed drugs
• Insect stings 
• Lupin
• Natural Rubber Latex (NRL)
• Flour contaminated by mites
• The oleosins in sesame
• Exercise induced anaphylaxis (EIA)
• Cold induced urticaria / anaphylaxis 
• Delayed allergy to red meat
• Idiopathic anaphylaxis  

Management 

1. Call for help
2. ABCD assessment
3. Intramuscular epinephrine (adrenaline)
• For adults: 500 micrograms IM (0.5 mL)
• For 6-12 year olds: 300 micrograms IM (0.3 mL)
• For under 6 year olds: 150 micrograms IM (0.15 mL)

Atopy

Also known as atopic syndrome.

 

Physiology

IgE and eosinophils are tools used by the immune system to fight macroparasitic diseases such as helminthiasis. IgE binds to an allergen and activates basophils, to release products including histamine. This causes a type 1 hypersensitivity reaction, also known as an allergic reaction. The size of the reaction can range from local symptoms (localised swelling, itching and redness), to systemic symptoms (angioedema, anaphylaxis).

Pathophysiology

A patient with atopy has a predisposition to produce high circulating levels of immunoglobulin E (IgE) and eosinophilia.

An atopic patient will usually have a history of one or more atopic diseases (see below). There are genetic factors, and there is often a strong family history of atopy.

This is a very common condition in highly developed societies. The hygiene hypothesis postulates that a low prevalence of parasitic infections causes a high prevalence of atopic disease, because there is insufficient modulation of the immune system without parasitic infection.

Atopic diseases

• Allergic rhinitis 
• Allergic conjunctivitis  
• Angioedema or anaphylaxis  
• Asthma
• Atopic dermatitis
• Drug allergy
• Eosinophilic esophagitis 
• Food allergy
• Urticaria

Atopy is associated with a rare vasculitis called eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome).

Eosinophilic granulomatosis with polyangiitis

Systemic vasculitis

Also known as 

EGPA or Churg-Strauss syndrome.

This disease is strongly associated with asthma, as they share common pathological features.

 

Pathological findings

• High levels of circulating IgE
• Eosinophilia