Prurigo

Author: Clin. Assoc. Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2009.


What is prurigo?

The term prurigo refers to intensely itchy spots. It may be used when the cause is known (see list below) or to describe a condition of unknown cause characterised by small itchy bumps.

Prurigo should be distinguished from pruritus (itch), in which there are no primary skin lesions.

What does prurigo look like?

Prurigo has primary and secondary skin lesions.

  • Primary prurigo lesions are dome-shaped papules.
  • Secondary prurigo lesions are scratched papules, scaly lesions, or thickened, darkly pigmented areas (lichen simplex or neurodermatitis). Scratching may lead to scarring.
Prurigo

Prurigo simplex

Prurigo simplex presents as symmetrically distributed, small, intensely itchy, dome-shaped bumps. Sometimes there are tiny blisters. They are most numerous on the outer aspects of the limbs and buttocks, but may occur anywhere on head and neck, trunk and limbs. Prurigo may affect children and adults.

Aternative names for prurigo simplex include chronic prurigo of adults, prurigo mitis, and Hebra prurigo. When the spots are dark in colour, it may be called prurigo pigmentosa.

Often the primary prurigo papule is no longer visible because scratching has removed it. Prurigo may cause considerable distress because severe itch can prevent sleep.

Prurigo

Nodular prurigo

Nodular prurigo presents with hard warty nodules, often showing increased pigmentation. As they are very itchy, they are often ulcerated or crusted. Nodular prurigo is very resistant to treatment.

Prurigo pigmentosa

Prurigo pigmentosa is characterised by an itchy rash with a net-like pigmentation.

Associated conditions

In some people, prurigo is associated with another skin condition or health problem. These include:

Treatment of prurigo

Treatment may include the following diverse agents.

More severe disease may be treated with immune suppressive agents.

Severe itch may be relieved by centrally acting medicines. These include:

  • Tricyclic antidepressants such as amitriptyline
  • Anticonvulsants such as gabapentin, pregabalin or sodium valproate
  • Opiate antagonists such as naltrexone.

What investigations should be done?

As there are several skin conditions that present with prurigo, investigations may be necessary to make the diagnosis.

Skin biopsy is often performed to look for specific features of dermatitis herpetiformis, which are diagnostic of that condition. Direct immunofluorescence is also diagnostic for dermatitis herpetiformis. The histology of other forms of prurigo may be nonspecific, or show hyperkeratosis (scale), acanthosis (skin thickening) and inflammatory infiltrate (lymphocytes in the dermis).

Blood tests may include general health screening and indirect immunofluorescence tests.

  • Blood count
  • Renal function
  • Liver function
  • Immunoglobulins
  • Protein electrophoresis
  • Skin antibodies
  • Thyroid function tests

Chest X-ray, CT scan or MRI may also be ordered. Further tests will depend on the results of initial screens.

Other types of prurigo

Itchy prurigo papules may arise in several other skin disorders.

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