Relatively uncommon

Prurigo Nodularis (picker’s nodules)

Introduction

Prurigo nodularis (PN) is a condition of unknown origin presenting with both pruritus and characteristic nodules, anywhere on the skin but especially on the abdomen, extremities or in the pubic or vulvar areas, in the hair-bearing epithelium. It is usually impossible to determine whether itching came first and the nodules followed, or the nodules caused itching.1

Epidemiology

Prurigo nodularis has been identified in all age groups and races and both genders, although it is most common in older people.2

Etiology

The etiology is unknown. In some cases, underlying diseases bring about chronic itching, which may start the process off. The following conditions have been associated with prurigo nodularis:

  • Hepatic or renal dysfunction
  • Local trauma or insult to the skinInfection
  • Infestation
  • HIV/immunodeficiency
  • Personal or family history of atopic dermatitis
  • Celiac disease
  • Autoimmune disorders
  • Anxiety or other psychiatric condition

It is generally thought that, whatever the initial cause, chronic “picking” at the skin is a behavioral component that perpetuates and exacerbates the lesions and the itching (similar to the itch/scratch/itch cycle of lichen simplex, which may occur alongside of PN).3

Repetitive rubbing, scratching, and picking at the skin (induced by a foreign body, underlying associated disease, or self-inflicted) results in plaque or nodular lichenification and hyperkeratosis. Pigmentary changes often result from the repetitive trauma to the skin, as well.

Symptoms and clinical features

With prurigo nodularis, a person feels intense pruritus at discrete points and cannot control the urge to rub, scratch, or pick at these points on the body. Any abnormality or explanation for the pruritus is usually impossible to identify, although the scratching reaction is obvious. The patient presents with a hard nodule or nodules, usually 0.5 to 1.5 cm in diameter. Discrete, nodular, hyperpigmented/purpuric lesions with surfaces that are scaly, excoriated, and possibly crusted, surrounded, usually, by an irregular, hyperpigmented ring are seen.

Prurigo nodularis

Mature nodules rarely increase or decrease in size; spontaneous resolution is rare. Prurigo nodularis is usually bilaterally symmetric, with nodules that are either stable or increasing in number.

Despite the known association with various conditions (list above), patients may have no significant medical or psychiatric history. At the same time, many practitioners believe that there is a strong psychological component involved with this condition.

Diagnosis

Diagnosis is made clinically, aided by the patient’s admission of chronic itching and picking at the skin. Biopsy may be done to rule out squamous cell carcinoma or infection, especially deep fungal or mycobacterial infection.

If underlying disease is suspected, the following tests may be done:4

  • Complete blood count
  • Renal function tests (urea, creatinine, and electrolytes)
  • Liver function tests and serology for hepatitis
  • Thyroid and parathyroid hormones
  • Total serum IgE levels
  • Patch test
  • HIV test and Mantoux test (if indicated)

Pathology/laboratory findings

Histologically, PN is characterized by marked hyperkeratosis, focal parakeratosis, and marked irregular acanthosis that is often of pseudoepitheliomatous proportions. The characteristic neurological changes observed include hypertrophy and proliferation of dermal nerves.5 There may be non-specific inflammation. In the search for a cause, studies have found increased Merkel cells, mast cells, dermal Langerhans cells, and neuropeptides that are thought to contribute to the disorder.6

Differential diagnosis

Hypertrophic lichen planus, multiple keratoacanthomas, pemphigoid nodularis, and nodular scabies can be considered.

Treatment/management

Identify possible underlying disease and, where possible, treat or refer for treatment. Folliculitis may be the initiating factor.

Psychological components can be addressed through cognitive behavioral therapy (CBT) or other habit-reversal therapy, including biofeedback and hypnosis.7 Some practitioners have found that adjunctive therapy with SSRIs prescribed for people with obsessive-compulsive disorder is very useful.8

Oral antihistamines such as promethazine hydrochloride 25–75 mg orally at night, or oral antidepressants such as doxepin 10–75 mg orally at night may be administered to reduce the pruritus.9

Potent topical glucocorticoid creams or ointments, such as betamethasone dipropionate 0.5 mg/g, can be helpful, but the thickness of the lesions may prevent the medication from being effective and may cause steroid-related side effects to adjacent tissue.

Intralesional triamcinolone acetonide 10 mg/mL, about 0.05 cc injected into individual lesions is effective.10

Cyrotherapy can be helpful temporarily because of the freezing action on the nerve cells.11 12 The total time of liquid nitrogen applied to the nodules varies from 10–30 s with two to four freeze–thaw cycles depending on the size of the nodule. Blistered nodules may take 2–4 weeks to heal and be replaced by hypopigmented macules.13 Itching may be relieved for as much as three months.

A combination of cryosurgery, intralesional triamcinolone acetonide 40 mg/mL diluted 1:3 with lidocaine 1% may be an effective method for treatment of PN. The immediate post-cryosurgical erythema that develops as the thaw wears off represents an edematous state that facilitates the injection of triamcinolone acetonide.14

Occlusive bandages may be useful.

Other treatment modalities:

Topical application of capsaicin (0.05–0.1%), applied 4-6 times a day for 2 weeks to 10 months can be effective in the very early manifestations. However, the frequency of the dosing and the burning that accompanies it, are disadvantages. The condition is likely to recur.15

Ultraviolet light, cyclosporine, and thalidomide have also been used with good effect but with significant side effects.16

References

  1. Soter NA. Nummular eczema and lichen simplex chronicus/prurigo nodularis. In: Freedberg IM, Eisen AZ, Wolff K, Austen KF, Goldsmith LA, Katz SI, eds. Fitzpatrick’s dermatology in general medicine, Vol. 1, 6th edn. New York:McGraw-Hill USA, 2003: 1194–1198.
  2. Lotti T, Buggiani G, and Prignano, F. Prurigo nodularis and lichen simplex chronicus. Dermatologic Therapy. 2008. Vol. 21; 42–46
  3. Lotti T, Buggiani G, and Prignano, F. Prurigo nodularis and lichen simplex chronicus. Dermatologic Therapy. 2008. Vol. 21; 42–46
  4. Lotti T, Buggiani G, and Prignano, F. Prurigo nodularis and lichen simplex chronicus. Dermatologic Therapy. 2008. Vol. 21; 42–46
  5. Lee MR, Shumack S. Prurigo nodularis: a review. Australas J Dermatol. 2005 Nov; 46(4):211-218.
  6. Lee MR, Shumack S. Prurigo nodularis: a review. Australas J Dermatol. 2005 Nov; 46(4):211-218.
  7. Shenefelt PD. Biofeedback, cognitive-behavioral methods, and hypnosis in dermatology: is it all in your mind? Dermatol Ther. 2003:16: 114–122.
  8. Lynch PJ. In Red Papules and Nodules, in Edwards L and Lynch PJ. Genital Dermatology Atlas, 2nd ed. 2011. Wolters Klewer/Lippincott, Williams, and Wilkins. Philadelphia. 89.
  9. Lotti T, Buggiani G, and Prignano, F. Prurigo nodularis and lichen simplex chronicus. Dermatologic Therapy. 2008. Vol. 21; 42–46
  10. Lee MR, Shumack S. Prurigo nodularis: a review. Australas J Dermatol. 2005 Nov; 46(4):211-218.
  11. Lynch PJ. In Red Papules and Nodules, in Edwards L and Lynch PJ. Genital Dermatology Atlas, 2nd ed. 2011. Wolters Klewer/Lippincott, Williams, and Wilkins. Philadelphia. 89.
  12. Waldinger TP, Wong RC, Taylor WB, Voorhees JJ. Cryotherapy improves prurigo nodularis. Arch. Dermatol. 1984; 120: 1598–1600.
  13. Lee MR, Shumack S. Prurigo nodularis: a review. Australas J Dermatol. 2005 Nov;46(4):211-218.
  14. Stoll DM, Fields JP, King LE. Treatment of prurigo nodularis: use of cryosurgery and intralesional steroids plus lidocaine. J. Dermatol. Surg. Oncol. 1983; 9: 922–924.
  15. Lotti T, Buggiani G, and Prignano, F. Prurigo nodularis and lichen simplex chronicus. Dermatologic Therapy. 2008. Vol. 21; 42–46
  16. Lee MR, Shumack S. Prurigo nodularis: a review. Australas J Dermatol. 2005 Nov;46(4):211-218.