Thunderstorm Asthma

Thunderstorm asthma is an epidemic of acute asthma that follows thunderstorms during the pollen season, mainly in people sensitised to grass pollen (and in some regions to Alternaria). It can overwhelm emergency services.

Pathophysiology. Storm winds and humidity lift pollen grains, which rupture on contact with moisture and release small respirable particles (starch granules and pollen fragments) that carry allergen into the lower airway. Large numbers of sensitised patients then develop acute bronchoconstriction within hours.

Most affected people have allergic rhinitis with grass pollen sensitisation. Many have no previous asthma diagnosis or have poorly controlled asthma.

Events follow a pattern of high pollen counts, a thunderstorm outflow, and a sudden rise in presentations within 30 minutes to hours.

• Sudden cough, wheeze and breathlessness during or after a storm
• Rapid deterioration within hours
• Prior seasonal rhinitis, with no or mild past asthma
• Chest tightness and hypoxia in severe cases
• Respiratory failure and death in a minority
• Multiple presentations at the same time in an area

• Clinical diagnosis by timing (storm, pollen season), symptoms and wheeze.
• Severity assessment: respiratory rate, speech, oxygen saturation, peak flow, and arterial gas in severe cases.
• Chest X-ray for atypical presentations or severe cases, to exclude pneumothorax or infection.
• Later evaluation: spirometry with reversibility, skin prick test or specific IgE to grass pollen and other allergens, and fractional exhaled nitric oxide.
• Exclusion of cardiac causes and pulmonary embolism when features are atypical.

Differential diagnosis.

• Acute exacerbation of known asthma from another trigger
• Viral respiratory infection
• Anaphylaxis
• Heart failure and pulmonary embolism
• Vocal cord dysfunction and panic attack
• Pneumonia and pneumothorax

• Acute attack: oxygen to keep saturation at 94 to 98%, and salbutamol 4 to 10 puffs (100 microgram each) by pressurised inhaler with spacer, repeated every 20 minutes for the first hour (or 5 mg nebulised).
• Corticosteroid: prednisolone 40 to 50 mg orally daily for 5 days (children 1 to 2 mg/kg, maximum 40 mg).
• Severe attack: add ipratropium 500 microgram nebulised, magnesium sulfate 1.2 to 2 g intravenously over 20 minutes, and arrange escalation to high dependency or intensive care.
• Long term control: regular inhaled corticosteroid with formoterol (for example budesonide with formoterol 200/6 microgram, 1 to 2 inhalations twice daily, with the same inhaler as reliever), with a written action plan.
• Prevention: treat grass pollen rhinitis with intranasal corticosteroid, start inhaled corticosteroid before the pollen season in at risk patients, and consider grass pollen immunotherapy (sublingual tablet 75,000 SQ-T once daily, started 12 to 16 weeks before the season).
• Avoidance on storm days in season: stay indoors with windows closed, use air conditioning with recirculation, and keep medication at hand.
• Public health: pollen forecasts and thunderstorm warnings, and emergency service planning.

Special groups.

• Patients with seasonal rhinitis but no asthma diagnosis: carry a reliever and know the plan on storm days.

Monitoring. Review within 2 days of an attack and again at 1 to 2 weeks. Spirometry once stable. Review before each pollen season.

Referral and escalation. Refer to respiratory medicine or allergy after an attack, for diagnosis, immunotherapy and long term control. Emergency for severe breathlessness, silent chest or oxygen saturation under 92%.