Sensory Hyperreactivity Patients May Suffer from Neurochemical Alteration

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http://ehp.niehs.nih.gov/press/060405b.html

July 5, 2005

CONTACT: Jim Tobin

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Sensory Hyperreactivity Patients May Suffer from

Neurochemical Alteration

Report in Environmental Health Perspectives finds

sensory hyperreactivity could be the true cause of

airway irritation

[Research Triangle Park, NC] For the first time,

scientists have uncovered a link between patients with

increased sensitivity to scents and chemicals--a

condition known as sensory hyperreactivity (SHR)-- and

a physiologic response, according to a study published

in the July 2005 issue of the peer-reviewed journal

Environmental Health Perspectives (EHP). This study

confirms that some chemically intolerant people with a

history of coughing and upper- and lower-airway

symptoms can connect their symptoms to a clear and

measurable neurochemical alteration in airway mucosa.

SHR-related symptoms such as throat irritation, eye

irritation, excess phlegm production, and coughing

have often been mistakenly attributed to allergies or

asthma. The authors stress that although the symptoms

may be similar, there is a distinct need to “emphasize

the discrepancy between [sHR and allergies/asthma],

though these groups have similar airway symptoms and

are often confused.”

The primary difference between patients with

allergies/asthma and those with SHR is the absence of

mucosal inflammation among the latter. Among

allergy/asthma sufferers, this inflammation results in

high levels of nerve growth factor (NGF), a protein

that is essential for the survival and development of

sensory neurons.

The authors hypothesized that a neurochemical

alteration lay at the root of SHR. Although SHR

patients do not experience mucosal inflammation (a

source of high NGF levels), they have been shown to

have an increased cough sensitivity to inhaled

capsaicin (the hot ingredient in chili peppers).

Capsaicin is known to stimulate sensory nerve endings

and induce coughing when inhaled. The researchers

therefore theorized that the NGF reaction in SHR

patients “may be derived from hyperreactive nerve

endings.”

The researchers studied 13 nonsmoking patients who had

been referred to an asthma and allergy clinic due to

symptoms suggestive of those conditions, but for whom

allergy tests were negative and asthma medications

ineffective. The subjects were given increasing levels

of nebulized capsaicin. After this provocation, the

subjects’ coughs were counted and levels of NGF in

nasal discharge measured. Results were then compared

to a control group of 14 participants without a

history of allergies/asthma or respiratory

difficulties.

Within the study, all subjects exhibited a

dose-dependent response to inhaled capsaicin. However,

the SHR group coughed significantly more than the

control group. The SHR group also exhibited other

symptoms from the capsaicin inhalation including

throat irritation, heavy breathing, eye irritation,

excess phlegm production, and runny nose, while the

control group registered few or no additional

symptoms. The authors observed a significant

correlation between the number of coughs, change in

NGF levels, and symptom scores for throat irritation,

phlegm production, and runny nose.

According to the article, “patients with SHR do have

enhanced cough sensitivity to inhaled capsaicin, which

correlates to a small but significant increase in NGF

in nasal lavage fluid after capsaicin provocation.

This indicates a neurochemical imbalance of the

respiratory system in patients with SHR.” In other

words, the neurochemical imbalance causes SHR

sufferers to react abnormally to chemicals and scents,

even in “concentrations normally regarded as

harmless,” the study says.

The lead author of the study was Eva Millqvist. Other

authors included Ewa Ternesten-Hasseus, Arne Stahl,

and Mats Bende. Funding sources for the research as

reported by the authors included the Asthma and

Allergy Research Group, Department of Respiratory

Medicine and Allergy, Sahlgrenska University Hospital,

Göteborg, Sweden, and the Allergy Centre, Central

Hospital, Skövde, Sweden. The article is available

free of charge at

http://ehp.niehs.nih.gov/members/2005/7657/7657.html.

EHP is published by the National Institute of

Environmental Health Sciences, part of the U.S.

Department of Health and Human Services. EHP is an

Open Access journal. More information is available

online at http://www.ehponline.org/. Brogan & Partners

Convergence Marketing handles marketing and public

relations for EHP, and is responsible for creation and

distribution of this press release.

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