Rocked by thunderstorm asthma

Thunderstorm asthma may be related to the sudden and widespread breaking open of pollen grains in the atmosphere

I suspect I wasn’t the only one taken aback at the six deaths in Melbourne due to a condition known as thunderstorm asthma. Hundreds more were hospitalised, about one-third of whom had no history of diagnosed asthma, when the severe thunderstorm hit Australia’s second-largest city on Monday, November 21st. The city’s ambulance service responded to more than 1,870 cases of acute breathing problems.

Prof George Braitberg, head of the Royal Melbourne Hospital’s emergency department, likened the scene in the hospital to a war zone. “I’ve been an emergency physician for about 35 years, worked in a number of hospitals, and I can say, hand on heart, that I have not seen this before,” Braitberg said.

It is the Southern Hemisphere’s seasonal equivalent of our May/June and so it is peak pollen season “down under”. It seems grains of ryegrass pollen swelled up with the torrential rain before exploding into the atmosphere when the heavy storm hit. The tiny pollen particles then entered people’s lungs, causing the airways to tighten up and narrow.

Until now the largest outbreak of thunderstorm asthma occurred in London on June 24th, 1994. In a 30-hour period, 640 patients with asthma or other breathing problems swamped hospital emergency departments. This was more than 10 times the usual number of people requiring hospital treatment for asthma in an equivalent period.

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Causes

There is no scientific agreement on the precise causes and mechanisms behind thunderstorm asthma. But it does seem to be related to the sudden and widespread breaking open of pollen grains in the atmosphere. Each grain can release more than 500 granules, which are highly allergenic. And because they are smaller than pollen particles they are able to penetrate deep into the lungs. It is likely that those who usually suffer nasal and eye symptoms as part of an allergy may, for the first time, develop wheeze and other asthma symptoms due to this deeper airway penetration.

A review article published earlier this year in the journal Clinical and Experimental Allergy confirmed the pollen-bursting hypothesis. "During the first 20-30 minutes of a thunderstorm, patients suffering from pollen allergies may inhale a high concentration of the allergenic material that is dispersed into the atmosphere which, in turn, can induce asthmatic reactions, often severe," the authors said. They advise that everyone known to have a pollen allergy "should be alerted to the danger of being outdoors during a thunderstorm in the pollen season, as such events may be an important cause of severe exacerbations."

Panic attack

I have personally never seen a case of thunderstorm asthma. However, I do remember a house call I was on while a medical student on elective in west Cork. The doctor was called to see a woman in her 50s who, it emerged, was having a severe panic attack. It had been a thundery afternoon with several rolling thunderstorms. She had a thunderstorm phobia and was literally trembling under the bedclothes when we arrived. Although she did not have any respiratory problems, she was convinced the thunder and lightning represented a real threat to her wellbeing.

And although there is no scientific evidence to back the theory up, many of my patients with arthritis have accurately predicted the imminent arrival of a storm. Could it be due to a drop in barometric pressure, which often precedes a storm, causing joints to swell?

Meanwhile, the fact that most thunderstorms that occur at times of high pollen levels do not trigger a community-wide asthma outbreak suggests we are missing some vital piece in the causative jigsaw.

What about a link to climate change? Earlier this year a report predicted that climate change is causing more storms. More thunderstorms make it likely we will see these severe asthma “epidemics” more often. But there is, as yet, no evidence to suggest a cause and effect relationship between climate change and thunderstorm asthma.

mhouston@irishtimes.com @muirshouston