Multiple chemical sensitivity (MCS)--differential diagnosis in clinical neurotoxicology: a German perspective.

The multiple chemical sensitivity syndrome (MCS) is a new cluster of environmental symptoms which have been described and commented on for more than 15 years now in the USA. In the meantime it has also been observed in European countries. The main features of this syndrome are: multiple symptoms in multiple organ systems, precipitated by a variety of chemical substances with relapses and exacerbation under certain conditions when exposed to very low levels which do not affect the population at large. There are no lab markers or specific investigative findings. In our view, MCS is not a separate clinical syndrome but a collective term. A very small part of the patients in question may actually exhibit a somatic or psychosomatic response to low levels of a variety of chemicals in the environment. For another part, even if the MCS symptoms are induced by chemical substances in the environment, the basic hypersensitivity is a psychological stress reaction. In the third and largest group, the patients have been misdiagnosed, i.e. a somatic or psychiatric disease has been overlooked. There is a fourth group of patients in whom there is no evidence of any exposure at all but instead a belief system installed by certain physicians, the media and other groups in society. This paper tries to describe the neurological and neurotoxic aspects of MCS problems and to illustrate it with examples of an alleged outbreak of chronic neurotoxic disease caused by pyrethroids in Germany. Research strategy should establish clearly determined diagnostic criteria, agreement on the use of specific questionnaires as well as clinical and technical diagnostic procedures, prospective clinical studies of MCS patients and comparative groups as well as experimental approaches.