A middle-aged man presented with pruritus ani (i.e. irritation of the skin around the anus) for several months. He had been healthy and well until he developed a bad bout of diarrhoea from a trip to a nearby country half a year ago, where he has spent a week with other volunteers helping to build a school in a rural district.

A course of antibiotics helped cure his diarrhoea, but stool sent for microscopy for ova, cysts and parasites had been reported positive for “worm eggs”, for which he also received a course of albendazole.

His symptoms of pruritis ani started soon after, worse at night and in the early mornings, but not associated with any diarrhoea, fever or weight loss. Clinical examination was unremarkable. He had subsequently seen several doctors without lasting improvement – at least two repeat tests for parasites in the stool were negative, and a repeat course of albendazole had relieved his symptoms for a week, after which it had retired again. He claimed that he had found a few fine, threadlike worms on occasion in his underpants, visible with a magnifying glass, but had not brought any for demonstration.

His family was otherwise well and had no similar symptoms.

Question:

1. What is the diagnosis and how should this man be managed?

[Updated 30 April 2017]

This is not an infectious disease at all, but rather, delusional parasitosis. In this condition, the person has a fixed but false belief that he or she is infested with parasites, and often has the sensation of these parasites crawling on their skin. It is an extremely challenging condition to treat, since the patients believe that they have an organic condition, but the doctors feel that they have a psychiatric condition. Treatment involves establishment of a therapeutic alliance, followed by administration of psychotropic drugs. A case series was published in Singapore more than 10 years ago, highlighting the challenges of therapy.