What is prurigo pigmentosa?
Prurigo pigmentosa is a rare inflammatory skin condition of unknown cause. It is characterized by a recurrent itchy rash with netlike hyperpigmentation. It responds well to tetracycline, and has an excellent prognosis.
Prurigo pigmentosa is also known as Nagashima disease.
What causes prurigo pigmentosa?
The exact cause of prurigo pigmentosa is unknown but several mechanisms have been proposed, including friction with clothes or a contact allergy to trichlorphenol, chromium in acupuncture needles, chrome in detergent, and nickel.
It has been associated in some patients with ketotic states associated with diabetes, fasting and post-bariatric surgery
Who gets prurigo pigmentosa?
Prurigo pigmentosa has been described in people of all ages, gender and ethnicities. However, it is more common amongst Asians, particularly young women. Women are affected twice as commonly as men.
In some patients, prurigo pigmentosa has been associated with systemic diseases such as Sjogren syndrome, and eating disorders such as anorexia nervosa. It has also been described in people with atopy, as well as in pregnancy.
How does prurigo pigmentosa present?
Clinical features of prurigo pigmentosa include:
- A pruritic (itchy) rash, which may recur
- Inflamed, red raised spots (papules) that merge to form a reticulate (network-like) pattern
- A symmetrical distribution on trunk with a preference for the upper back, sacrum (natal cleft), abdomen and chest
- It rarely involves the face or limbs
- Sparing of mucous membranes, hair and nails
- The papules resolve to leave a flat, reticulated (network-like) hyperpigmented (dark brown) pattern.
Histopathology of prurigo pigmentosa
There is a distinct histopathology in prurigo pigmentosa.
- Early lesion: superficial perivascular neutrophilic infiltrate, and a few necrotic keratinocytes
- Developed lesion: patchy lymphocytic infiltrate, and necrosis of numerous keratinocytes
- Late lesion: lymphocytic infiltrate, scale-crust, and melanophages
What is the treatment for prurigo pigmentosa?
Dapsone and tetracycline antibiotics are effective in treating prurigo pigmentosa during the inflammatory phase of the disease. These treatments are thought to work by interfering with the movement and function of neutrophils. Recently macrolide antibiotics such as erythromycin have also been demonstrated to be helpful.
To date there are no effective treatments for the hyperpigmentation that develops in the later stages of the disease. It eventually fades.