Allergies

Medicine > Respiratory

Differential Diagnosis Schema 🧠

IgE-Mediated Allergies

Allergic rhinitis: Seasonal or perennial symptoms, nasal congestion, itching, sneezing, often associated with conjunctivitis.
Asthma: Wheezing, breathlessness, chest tightness, and cough, often with a history of atopy.
Anaphylaxis: Acute onset of symptoms involving multiple organ systems, such as skin (urticaria), respiratory (bronchospasm), cardiovascular (hypotension), and gastrointestinal (vomiting).
Food allergies: Immediate onset of oral pruritus, swelling, urticaria, or anaphylaxis following ingestion of a particular food.

Non-IgE-Mediated Allergies

Food protein-induced enterocolitis syndrome (FPIES): Delayed vomiting and diarrhea after ingestion of specific foods, primarily affecting infants and young children.
Contact dermatitis: Erythematous, itchy, and vesicular rash developing hours to days after exposure to allergens like nickel, latex, or poison ivy.
Celiac disease: Chronic gastrointestinal symptoms like diarrhea, weight loss, and malabsorption associated with gluten ingestion.

Mixed IgE and Non-IgE Mediated Allergies

Eosinophilic esophagitis: Chronic, immune/antigen-mediated esophageal condition with symptoms of food impaction, dysphagia, and reflux-like symptoms that do not respond to acid suppression.
Atopic dermatitis: Chronic, relapsing inflammatory skin condition characterized by pruritus, eczematous lesions, often with a history of atopy.
Allergic contact dermatitis: Combination of immediate and delayed hypersensitivity reactions causing a pruritic rash after allergen contact.

Non-Allergic Hypersensitivity Reactions

Non-allergic rhinitis: Chronic nasal congestion, rhinorrhea, or sneezing without an identifiable allergen.
Aspirin-exacerbated respiratory disease (AERD): Asthma, chronic rhinosinusitis with nasal polyps, and respiratory reactions following aspirin or NSAID intake.
Irritant contact dermatitis: Skin irritation and inflammation resulting from direct chemical or physical insult, without immunological involvement.
Lactose intolerance: Gastrointestinal discomfort, bloating, and diarrhea after lactose ingestion due to lactase deficiency.

Key Points in History 🥼

Presenting Symptoms

Onset, duration, and frequency of symptoms: Important to determine if the reaction is acute or chronic, episodic or persistent.
Nature of symptoms: Rash, respiratory difficulty, gastrointestinal symptoms, etc., which help narrow down the type of allergic reaction.
Trigger exposure: Identifying potential allergens such as foods, environmental factors, medications, or insect stings.
Seasonality of symptoms: Suggestive of allergic rhinitis or asthma if symptoms worsen during specific times of the year.

Background

Past medical history: History of atopic conditions such as asthma, eczema, or hay fever.
Family history: Presence of allergic conditions in close relatives, indicating a genetic predisposition.
Drug history: Recent use of medications, especially antibiotics, NSAIDs, or new prescriptions, which might be the cause of drug allergies.
Social history: Occupational exposures, smoking, and pets, which may contribute to or trigger allergic reactions.
Dietary history: Particularly relevant in food allergies; consider recent changes in diet.

Possible Investigations 🌡️

Initial Tests

Skin prick testing: Identifies immediate IgE-mediated allergic reactions to specific allergens.
Specific IgE blood tests: Measures the level of IgE antibodies to specific allergens in the blood.
Full blood count (FBC): Eosinophilia may indicate an allergic or parasitic process.
Total IgE levels: Elevated in various allergic conditions, though non-specific.
Patch testing: Used to identify allergens in non-IgE-mediated contact dermatitis.

Further Investigations

Oral food challenge: Conducted under medical supervision to diagnose food allergies, especially when the diagnosis is unclear from history and initial tests.
Spirometry: Assess lung function in patients with suspected allergic asthma.
Bronchial challenge test: Assesses airway hyperreactivity to inhaled allergens or irritants.
Endoscopy and biopsy: Used in eosinophilic esophagitis to assess esophageal inflammation and eosinophil count.
Component-resolved diagnostics (CRD): Advanced testing that identifies specific allergenic proteins to refine diagnosis and management.

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