Nodular prurigo or Prurigo nodularis is a very itchy dermatosis of unknown etiology. It is characterized by:
* Firm nodules, 1–3 cm in diameter, often with a verrucous surface.
* Crusting and scaling may cover recently scratched lesions.
* Older lesions may be darker or paler than surrounding skin.
* Distribution is usually bilateral symmetrical. The lumps usually start on the forearms and legs, and are worse on the outer aspects. The trunk, face and even palms can also be affected.
* Sometimes, the nodules are most obvious on the cape area (neck, shoulders and upper arms).
* The nodules are grouped and numerous but may vary in number from 2–200.
* New nodules appear from time to time, but existing nodules may regress spontaneously to leave scars.
* PN Can occur at all ages but mainly in adults aged 20–60 years.
* Both sexes are equally affected.
* The course often is long and can lead to significant stress and depression.

Etiology
* The cause is unknown. It is uncertain whether scratching leads to the lumps, or if the lumps appear before they are scratched.
* Up to 80% of patients have a personal or family history of atopic dermatitis, asthma or hay fever (compared to about 25% of the normal population).
* PN may start as an insect bite reaction or another form of dermatitis.
* PN has been associated with internal or cutaneous disease including:
1. Iron deficiency anemia
2. Chronic renal failure
3. Gluten enteropathy
4. HIV infection and many other diverse conditions.
5. Brachioradial pruritus (due to compression or traction of spinal nerves).

Investigations
1. Skin biopsy: the diagnosis of PN is primarily clinical and may be confirmed by skin biopsy which shows enormously thickened skin that may appear quite abnormal, sometimes resembling squamous cell skin cancer. The nerve fibers and nerve endings in the skin are markedly increased in size.
2. Direct immunofluorescence is usually negative.
3. Other investigations are important to be arranged to identify underlying diseases that are associated with nodular prurigo such as: CBC, LFTs, RFTs and TFTs.

Treatment
PN is one of the resistant dermatoses to be amenable to treatment. Local treatments tried include:
1. Emollients applied liberally and frequently to cool and soothe itchy skin – menthol or phenol may be added. Oral antihistamines may be given at night to reduce itch and allow sleep.
2. Ultrapotent topical steroids under occlusion. Corticosteroid injections (triamcinolone acetonide 10 – 40 mg /ml) into thicker nodules.
3. Coal tar ointment as steroid alternative.
4. Calcipotriol ointment may be more effective than topical steroids in some cases.
5. Capsaicin cream, which induces itching and burning until eventually the itch stops completely – it requires repeated applications four to six times daily.
5. Cryotherapy, which may shrink the nodules and reduce their itch.
6. Pulsed dye laser, which may reduce the vascularity of individual lesions.

Systemic treatments: may be helpful for more severe disease. Combination treatment is frequently recommended.
1. Phototherapy (UVB and PUVA)
2. Tricyclic anti-depressants such as amitriptyline or doxepin
3. Anticonvulsants used for neuropathic pain and itch, such as gabapentin or pregabalin
4. Naltrexone, an opiate antagonist has been reported to reduce itching in some subjects.
5. Oral steroids
6. Methotrexate
7. Thalidomide (reserved for very severe cases)
8. Ciclosporin, which may reduce the lumps and the itching but its use is limited by side effects.
9. Systemic retinoids such as acitretin or isotretinoin, which may shrink the nodules and reduce the severity of the itch.