Prurigo

What is Prurigo?

The term prurigo refers to acute itchy spots. It can be used when the cause is known (see list below) or to describe the condition of unknown cause characterized by small itchy bumps. Prurigo should be distinguished from pruritus (itching), where there is no initial lesion of the skin.

What does Prurigo look like?

Prurigo has primary and secondary skin lesions.

The primary prurigo lesions are dome-shaped papules.

Secondary Prurigo lesions are scratched papules, fibrous lesions or dense, dark pigmented areas (lichen simplex or neurodermatitis). There may be scratching spots.

Prurigo Simplex

The Prigigo Simplex presents as a symmetrically distributed, small, intense itch, dome-shaped bump. Sometimes there are small blisters. They are most common on the outside of the limbs and buttocks, but can occur anywhere on the head and neck, trunk and limbs. Prurigo can affect children and adults.

Alternative names for Prurigo Simplex include Chronic Prurigo for Adults, Prurigo Mites, and Hebra Prurigo. When the spots are dark in color, they can be called prurigo pigmentosa.

Often the primary Prurigo papule is no longer seen because scratching has removed it. Prurigo can cause considerable discomfort because severe itching can interfere with sleep.

Nodular prurigo

Nodular prurigo appears with hard warty nodules, often showing enlarged pigmentation. Since they are very itchy, they are often ulcerated or crusted. Nodular prurigo is very resistant to treatment.

Prurigo pigmentosa

Prurigo pigmentosa is characterized by an itchy rash with mesh-like pigmentation.

Relevant terms

In some people, prurigo is associated with other skin conditions or health problems. These include:

Atopic eczema (Besnir prurigo)

Bullas pemphigoid (pemphigoid nodularis)

Eczema (or dermatitis)

Papular urticaria (an allergic reaction to insect bites)

Iron deficiency

Thyroid disease

Human Immunodeficiency Virus Infection (HIV)

Pregnancy

Chronic renal failure

Diabetes

Polycythemia rubra vera

Hodgkin's lymphoma or non-Hodgkin's lymphoma

Drug abuse, especially amphetamines and cocaine

Damage to the spinal nerve

Treatment of prurigo

Treatment may include the following different agents.

Antihistamines, especially sedative agents that relieve itching

Intracranial corticosteroids

Systemic corticosteroids

Prolonged course of oral antibiotics, especially tetracycline

Dapson

Phototherapy

More serious diseases can be treated with immunosuppressive agents.

Methotrexate

Azathioprine

Cyclosporine

Medications that work centrally can relieve severe itching. These include:

Tricyclic antidepressants such as amitriptyline

Anticonvulsants such as gabapentin, pregabalin or sodium valproate

Opiate antagonists such as naltrexone.

What should be investigated?

Since there are different skin conditions present with prurigo, an investigation may be needed to diagnose the disease.

Skin biopsies are often performed to look for specific features of dermatitis herpetiformis, which is a diagnostic of that condition. Direct immunofluorescence is also diagnostic for dermatitis herpetiformis. Histology of other forms of prurigo may be indeterminate, or may show hyperkeratosis (scale), acanthosis (thickening of the skin), and inflammatory infiltration (lymphocytes of 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 test

Chest X-ray, CT scan or MRI can be done. Further testing will depend on the results of the initial screen.

Other types of prurigo

Itchy prurigo papules can occur in a variety of other skin diseases.

Infestation of scabies or lice on the body

Arthropod bites due to mosquitoes, sandflies, bedbugs and flies

Actinic prurigo (also called Hutchinson prurigo) - a form of light sensitivity in sunlit regions

Prior to pregnancy

Dermatitis herpetiformis - an immunobullous disease

Acne urticata

Reactive perforated collagenosis

Folliculitis

Mandatory skin picking

Psychosis, where patients experience delusions of formation (sensation of biting and crawling) or parasitosis