The differential diagnosis of self-injurious behavior in mentally retarded people.

Self-injurious behavior (SIB) is sometimes presented as if it were a unitary behavioral entity. It is this assumption that leads to impunity in clinical trials of SIB patients, who are thought to be a homogeneous group. In fact, nothing could be further from the truth. SIB is no more than the occasion for a neuropsychiatric differential diagnosis; first to consider environmental and medical circumstances that may induce SIB; then specific, diagnosable conditions from neurology and psychiatry; then specific syndromes like Lesch-Nyhan and Cornelia de Lange; and then for "idiopathic" cases, the alternative neuro-chemical hypotheses. The goal of differential diagnosis is not only to guide treatment, but also to improve subject homogeneity in clinical trials.