Delusional parasitosis and the matchbox sign revisited: the international perspective.

© 2010 The Authors. doi: 10.2340/00015555-0909 Journal Compilation © 2010 Acta Dermato-Venereologica. ISSN 0001-5555 The clinical presentation of delusional parasitosis, the fixed false belief of being infested by small creatures or inanimate particles, undergoes constant modulation by cultural phenomena as for the exact type of imaginary pathogens, but is otherwise very stable (1, 2). One of the key features is that patients bring specimens of alleged pathogens to the physician in order to prove that their skin, other parts of their body, or immediate environment are infested. This behaviour was first described by Perrin in 1896 (3). For this sign, an editorial in The Lancet in 1983 (4) proposed the name “the matchbox sign”, based on a report that many patients show their proofs of infestation carefully stored in matchboxes (5). With the advent of the internet in the late 1990s, patients started to use the web to find and share theories about their infection (6). They discuss how to make specimens for lay-research and exchange digital “proofs”. Since 2002, patients with this self-diagnosed so-called “Morgellons disease” have contacted dermatologists and microbiologists. They show the usual symptom constellation of patients with delusional parasitosis, but they blame fibres or filaments instead of living creatures for their infestation. The clinical spectrum of delusional parasitosis has been described by Lyell based on a survey among UK dermatologists in 1983 (5). However, this, and all other available surveys from the UK (7) and France (8) are old and were conducted only in single countries. Little is therefore known what exactly patients nowadays believe themselves to be infested with, and what they present as proofs of infestation, from the larger, international perspective. We therefore carried out the first international survey amongst psycho-dermatology experts in order to address these issues.