Mass psychogenic illness (MPI), also called mass sociogenic illness, mass psychogenic disorder, epidemic hysteria or mass hysteria, involves the spread of illness symptoms through a population where there is no infectious agent responsible for contagion. It is the rapid spread of illness signs and symptoms affecting members of a cohesive group, originating from a nervous system disturbance involving excitation, loss, or alteration of function, whereby physical complaints that are exhibited unconsciously have no corresponding organic causes that are known.
Causes
MPI is distinct from other types of collective delusions by involving physical symptoms. It is not well understood and its causes are uncertain. Qualities of MPI outbreaks often include: symptoms that have no plausible organic basis; symptoms that are transient and benign; symptoms with rapid onset and recovery; occurrence in a segregated group; the presence of extraordinary anxiety; symptoms that are spread via sight, sound or oral communication; a spread that moves down the age scale, beginning with older or higher-status people;
British psychiatrist Simon Wessely distinguishes between two forms of MPI:
Mass anxiety hysteria "consists of episodes of acute anxiety, occurring mainly in schoolchildren. Prior tension is absent and the rapid spread is by visual contact." Mass motor hysteria "consists of abnormalities in motor behaviour. It occurs in any age group and prior tension is present. Initial cases can be identified and the spread is gradual. ... [T]he outbreak may be prolonged."
While his definition is sometimes adhered to, others contest Wessely's definition and describe outbreaks with qualities of both mass motor hysteria and mass anxiety hysteria.
The DSM-IV-TR does not define a diagnosis for this condition but the text describing conversion disorder states that "In 'epidemic hysteria', shared symptoms develop in a circumscribed group of people following 'exposure' to a common precipitant."
Common symptoms
Timothy F. Jones of the Tennessee Department of Health compiles the following symptoms based on their commonality in outbreaks occurring in 1980–1990:
Prevalence and intensity
Adolescents and children are frequently affected in cases of MPI. The hypothesis that those prone to extraversion or neuroticism, or those with low IQ scores, are more likely to be affected in an outbreak of hysterical epidemic has not been consistently supported by research. Bartholomew and Wessely state that it "seems clear that there is no particular predisposition to mass sociogenic illness and it is a behavioural reaction that anyone can show in the right circumstances."
Intense media coverage seems to exacerbate outbreaks. The illness may also recur after the initial outbreak. John Waller advises that once it is determined that the illness is psychogenic, it should not be given credence by authorities. For example, in the Singapore factory case study, calling in a medicine man to perform an exorcism seemed to perpetuate the outbreak.
Research
Besides the difficulties common to all research involving the social sciences, including a lack of opportunity for controlled experiments, mass sociogenic illness presents special difficulties to researchers in this field. Balaratnasingam and Janca report that the methods for "diagnosis of mass hysteria remain contentious." According to Jones, the effects resulting from MPI "can be difficult to differentiate from [those of] bioterrorism, rapidly spreading infection or acute toxic exposure."
These troubles result from the residual diagnosis of MPI. There is a lack of logic in an argument that proceeds: "There isn't anything, so it must be MPI." It is an example of an argument from ignorance, with ignorance here intended to mean "an absence of contrary evidence". It precludes the notion that an organic factor could have been overlooked (i.e. that there may have been insufficient investigation), or the possibility that the answer may currently be unknown but known at a future point in time. Nevertheless, running an extensive number of tests extends the probability of false positives. Singer, of the Uniformed Schools of Medicine, has summarized the problems with such a diagnosis: [Y]ou find a group of people getting sick, you investigate, you measure everything you can measure ... and when you still can't find any physical reason, you say "well, there's nothing else here, so let's call it a case of MPI."