Prurigo nodularis
What is prurigo nodularis?
Prurigo nodularis is an intensely itchy, abraded (severely scratched-looking) rash characterised by discreet, thickened and leathery nodules or bumps. The condition usually occurs on the outer surfaces of the arms and legs. It is considered to be a localised form of lichen simplex chronicus which is a chronic condition characterised by itchy and thickened skin.
The condition occurs in all age groups and equal numbers of males and females are affected. Abrasions are usually pronounced. Affected people experience intense and periodic itch which is profoundly disabling. Under the microscope, the condition closely resembles eczema.
What does prurigo nodularis look like?
A nodule of prurigo nodularis is firm to the touch. It is usually appears as a large dome-shaped, wart-like growth up to 3 cm in diameter.
The lesions start as small, red, itchy papules or rounded skin bumps. Scratching leads to weeping ulcers which crust and scale. As the nodule ages, it often changes colour – usually brown-black but sometimes pale-coloured. The in-between skin can be dry and scaly.
Nodules usually occur in groups. These groups vary in number from singles to hundreds. They are distributed symmetrically, most commonly on the outer surfaces of the arms and legs. However, the face, trunk and even palms can be involved.
New lesions may continue to present and some existing nodules heal, usually leaving a scar.
What causes prurigo nodularis?
There is an identifiable cause in the majority of cases. In 50% of cases, an inherited condition such as asthma, eczema, hay fever or hives is present. This is known as “atopy”.
Prurigo nodularis can occur in stasis eczematous dermatitis (a common form of dermatitis of the lower legs which is associated with pooling or “stasis” of blood in the veins). It also occurs in those affected with nummular eczema (a common type of eczema with distinct, coin-shaped sores), lichen simplex and insect-bite reactions.
In rare cases, the condition can be seen with pemphigoid nodularis (a rare autoimmune skin disease which usually presents with big blisters) and dermatitis herpetiformis (an itchy blistering skin condition associated with coeliac disease).
In 30% of cases, a metabolic or biochemical cause induces itch such as:
- Nutritional deficiency
- Liver abnormality
- Uraemia (increased urea in the blood from insufficiency of the kidneys).
Less common causes are thyroid disease, neurologic disease (stroke), hypercalcaemia (high calcium in the blood) and lymphoma (cancer of the blood).
The remaining 20% of affected people have psychological factors such as depression, anxiety and/or psychosis.
Nutritional deficiency most often shows in the blood as decreased iron absorption. Most often, it is diet-related with added loss (i.e. underlying iron deficiency because of eating habits in a female with excess menstrual iron loss). Malabsorption of iron (compromised absorption of iron in the gut) can occur with gluten hypersensitivity but most commonly following bowel surgery. Gastrointestinal bleeding is another cause of iron deficiency.
Those affected with the prurigo nodularis often have all three causative factors (atopic, psychological and nutritional). Atopic dermatitis can be triggered and perpetuated by acute depression and then aggravated by nutritional problems – the “lonely, malnourished depressive”. The eczema tendency, depression and diet must all be treated – not only the itchy nodules.
How is prurigo nodularis diagnosed?
The condition is usually diagnosed from its clinical appearance as an extremely itchy dermatitis, characterised by persistent nodules.
Skin biopsy shows the microscopic picture of eczema. It differs from lichen simplex chronicus only by its dome shape.
How is prurigo nodularis treated?
Injected and topical steroids are the mainstay of therapy for the nodules.
Simple topical therapy is doomed to fail. Oral steroids are often necessary and are used in conjunction with super potent topical corticosteroids which are applied under plastic wrap to enhance their effect.
Other treatments include:
- Phototherapy (PUVA and UVB)
- Cryotherapy
- Antidepressants
- Systemic retinoids (such as acitretin)
- Naltrexone
- Thalidomide
What is the likely outcome of PN?
The condition is difficult to cure because it depends on the absolute resolution of the underlying disorder. Remission can be expected when the affected person is faithful to the treatment regime.
The course of prurigo nodularis is chronic. The affected person is often miserable. Suicidal tendencies can occur.
This information has been written by Dr Malcolm Lane-Brown
Updated 02 July 2015