Summary

This chapter explores puzzling paradoxes that apply to two major neurological diseases. The first involves allergies which range in severity from allergic rhinitis, which may cause only mild discomfort, to allergic asthma which can be life-threatening. It has been repeatedly demonstrated that people with malignant brain tumours have fewer allergies than people who do not. The reasons for this association are unknown, but it is possible that allergies reflect an active immune system that is also able to destroy nascent tumours. Alternatively, it is well known that malignant brain tumours suppress antitumour immunity, so it is possible that they suppress allergies as well. The second paradox involves cigarette smoking, well known to cause lung cancer, heart disease, chronic respiratory disease and other harmful effects that have been extensively documented. Yet cigarette smokers have a lower risk of Parkinson's disease than do people who have never smoked cigarettes. Epidemiologic evidence indicates that this paradox is not an artefact, but that cigarette smokers actually enjoy lower risks of Parkinson's disease as a result of smoking. These reduced risks probably result from nicotine's observed protective effects on the nervous system.

Introduction

Conventional wisdom maintains that an illness or assault on one organ should not have a beneficial effect on another. Yet in neurology, as in other branches of medicine, there are cases where harm to one biological system appears to benefit another. This chapter focuses on the protective effects of allergy on glioma, and of smoking on Parkinson's disease.