Asthma

Definition

Asthma is a heterogeneous, chronic inflammatory disease of the airways with bronchial hyperresponsiveness. It is characterized by wheeze, breathlessness, chest tightness and cough that vary in frequency and intensity, together with variable limitation of expiratory airflow. Unlike COPD, asthma often begins in childhood or adolescence, follows an episodic course, and the obstruction is often fully reversible.

Classification

• Type 2-high (eosinophilic): eosinophilic airway inflammation, often allergic.
• Type 2-low: neutrophilic or paucigranulocytic, without eosinophilic inflammation.
• NSAID-exacerbated respiratory disease (Samter triad): asthma, chronic rhinosinusitis with nasal polyps and hypersensitivity to cyclooxygenase-1-inhibiting analgesics.
• Level of asthma control: controlled, partly controlled or uncontrolled.

Occurrence & epidemiology

Worldwide an estimated 260 million people had asthma in 2021. In Germany the 12-month prevalence in adults in the GEDA 2014/2015 survey was 6.2 %, with women affected more often than men (7.1 % versus 5.4 %); in children and adolescents the KiGGS study found 4.0 %. In childhood boys are affected more often.

Aetiopathogenesis

Asthma arises from the interplay of numerous genes (e.g. the 17q21 locus with ORMDL3) and environmental factors. Risk factors are atopy, household and environmental allergens (house dust mites, cockroaches, pets, pollen), preterm birth and low birth weight, overweight, active smoking, low socioeconomic status and family history.

Triggers of exacerbations: allergens, cold dry air, infections, physical exertion, inhaled irritants, emotions, gastresophageal reflux disease, and cyclooxygenase-1-inhibiting analgesics (NSAIDs; in about 9 % of all people with asthma).

Pathophysiology: Th2 cells, eosinophils and mast cells form an inflammatory infiltrate in the epithelium and smooth muscle. This leads to bronchoconstriction, mucosal edema, hyperresponsiveness and airway remodeling with desquamation, subepithelial fibrosis, angiogenesis and smooth muscle hypertrophy.

Clinical features

• Episodic wheeze, breathlessness, chest tightness and cough; night-time waking in more severe asthma
• Often normal findings between episodes
• Exacerbation: wheeze, tachypnea, tachycardia, use of accessory muscles, upright posture, speech limited by breathlessness, prolonged expiration, pulsus paradoxus
• Impending respiratory failure: "silent chest" without audible wheeze, impaired consciousness, cyanosis, oxygen saturation below 90 %

Diagnosis

• Spirometry with reversibility testing: an increase in FEV1 of more than 12 % or more than 200 mL after a bronchodilator makes asthma likely; absent reversibility in a single test does not exclude it.
• Bronchial challenge (e.g. methacholine, exercise, cold air): with normal lung function and a well-founded suspicion; a fall in FEV1 of at least 20 % is relatively specific.
• FeNO: values above 50 ppb indicate asthma with high probability when the history fits; a low value does not exclude it.
• Allergy tests: skin prick test and/or specific IgE.
• Diffusing capacity: normal or raised in asthma, reduced in emphysema.
• Chest X-ray: usually normal, during exacerbations hyperinflation or segmental atelectasis from mucus; helps to exclude other causes.
• Peak flow: not sufficient on its own for the diagnosis.

Keep learning in the app

Further reading (open access)

1. Nationale VersorgungsLeitlinie Asthma, Langfassung (Version 5.0)
2. MSD Manual Profi-Ausgabe: Asthma
3. StatPearls: Asthma

Cross-references