MINNEAPOLIS-- Seasonal allergic rhinitis may produce cognitive deficits that cannot be explained by the use of antihistamines or other sedating drugs, a new study has found.[1] "Allergic patients reported slow or fuzzy thinking when not taking medications," lead study author Paul S. Marshall, PhD, recently told RESPIRATORY REVIEWS. "Some of these patients also reported problems with memory."

The study found evidence that allergic reactions slow thinking, but they do not appear to cause difficulties with attention or retention of information in most patients. However, allergic reactions may cause difficulties with learning in a significant subgroup of patients.

The study, one of only a few to examine the cognitive effects of allergic rhinitis, was a follow-up to a similar but much smaller investigation Dr. Marshall completed about seven years ago.[2] That study also linked rhinitis to cognitive impairment. "We went further in the present study by using a much larger battery of cognitive tests," pointed out Dr. Marshall, director of the neuropsychology section at Hennepin County Medical Center in Minneapolis.

The study included 32 patients (age 23 to 50 years) with seasonal allergic rhinitis and 25 nonatopic controls of similar ages. All rhinitis patients were ragweed-sensitive. Participants underwent cognitive testing during three ragweed seasons, from 1996 to 1998. Testing took place at the start of ragweed season after patients had experienced symptoms for four days. They were not permitted to take allergy medications at this time. Participants were also tested in the winter of 1997, when ragweed allergy was presumably not a concern.

During ragweed season, rhinitis sufferers displayed significant declines in speed of cognitive processing on Hick paradigm choice reaction time tests, which are taken on a computer and require rapid decisions in response to visual stimuli. Many, but not all, patients also had greater difficulty on the Buschke Selective Reminding Test, a test of working memory that requires subjects to memorize and recall word lists. However, the rhinitis sufferers showed no declines during ragweed season on several other tests of cognitive processing, memory, motor speed, or attention.

NOT JUST FATIGUE

From these findings, Dr. Marshall concluded that ragweed-induced allergic rhinitis causes subtle slowing of cognitive processing in many patients and difficulties in working memory in some. However, the mechanism of cognitive impairment in these patients remains a mystery.

"It could simply be fatigue related to poor sleep," Dr. Marshall suggested. "But I suspect there's also some direct biochemical process involved because I see these patients all the time and many don't report trouble sleeping."

One possibility is that ragweed allergy stimulates the release of cytokines, which have been shown to produce achiness and fatigue as well as cognitive impairment. Or it may interfere with adrenergic and cholinergic activity in the central nervous system, thereby impairing attention.

Whatever the cause, given that half of all patients with allergic rhinitis complain of cognitive difficulties during allergy season, further study is warranted.

--Timothy Begany

References
1. Marshall PS, O'Hara C, Steinberg P. Effects of seasonal allergic rhinitis on selected cognitive abilities. Ann Allergy Asthma Immunol. 2000;84:403-410.
2. Marshall PS, Colon EA. Effects of allergy season on mood and cognitive function. Ann Allergy. 1993; 71:251-258.