A case series of shared delusional infestation: folie à deux revisited.

Delusional infestation (DI) describes the unshakeable belief that one's skin is infected or infested with an external organism or inanimate material, in the absence of supportive medical evidence. It has been found that 5-26% of patients with DI will report similar symptoms in a close relative, which is known as shared DI or folie à deux. In some cases, more than one close relation may be affected. Shared psychotic disorder (SPD) appears as a distinct entity in the Classification of Mental and Behavioural Disorders (ICD-10)