Prurigo

• nodular prurigo is characterized clinically by intensely itchy nodules which may be associated with an eczematous eruption. Patients are frequently tormented by their symptoms which often prove difficult to control with conventional therapy (1)
• Clinical features:
  • occurs mainly in adults aged 20-60 years
  • affects both sexes equally
  • individual prurigo nodule is a firm lump, 1-3 cm in diameter - lesions often have a raised warty surface
    • early lesion may start as a smaller red itchy bump
    • crusting and scaling may cover recently scratched lesions
    • older lesions may be darker or paler than surrounding skin
    • there is often dry skin between the nodules
    • the lesions are intensely itchy - they are frequently excoriated and sometimes secondarily infected
    • lesions generally start on the lower arms and legs, and are worse on the outer aspects; other sites that may be affected include the trunk, face and palms
• Aetiology:
  • cause of nodular prurigo is unknown
    • atopy is found in 65–80% of patients in whom the disease may occur at an earlier age (1)
    • nodular prurigo has been associated with internal disease including iron deficiency anaemia, chronic renal failure, gluten enteropathy, HIV infection
• Investigations
  • occasionally skin biopsy is useful to confirm the diagnosis
    • histology may resemble lichen simplex but with greater hyperkeratosis
    • dense dermal infiltrate and vascular hyperplasia - these changes are likely to represent a non-specific reaction to scratching
  • direct immunofluorescence is usually negative
  • screening for associated diseases
    • blood tests may include full blood count, liver, kidney and thyroid function tests

Reference:

1. Woo PN et al. Br J Dermatol. 2000 Jul;143(1):215-6.