DISCUSSION
The correct diagnosis is prurigo nodularis (PN), which was first described in 1909 and has been extensively studied since. Though much remains unknown about PN, we know that, typically, the patient plays a major role in the genesis and perpetuation of the condition. In other words, these patients are pickers—but as they’ll tell you, they “wouldn’t pick if the lesions didn’t itch.” It does appear that they have a much lower threshold for itching than the general population.
Personal and family history of serious, ongoing bouts of depression and anxiety, as seen in this patient, are also typical among PN patients. Women appear to be far more likely to be diagnosed with PN, though there is no documentation of this in the literature.
These observations, while helpful for diagnosis, still don’t fully explain exactly why one person has PN while another doesn’t.
Besides the biopsy results, other keys to distinguishing PN include the characteristic lesions themselves, as well as the sparing of sites out of the patient’s reach. As is often the case, multiple old scars were seen on this patient’s upper back, confirming the chronicity of the condition.
In addition to educating patients about their role in the creation and perpetuation of PN, I find the most useful treatment to be intralesional triamcinolone in a 10-mg/cc strength (1/4 cc stock triamcinolone diluted in ¾ cc lidocaine), delivered directly into the lesion by 30-gauge needle Alternatively, a class 1 topical steroid cream (eg, clobetasol 0.05%) can be applied twice daily and then covered with a bandage. In cooler weather, when patients tend to bundle up, additional layers of clothing help to create a barrier that prevents patients from picking as much.
New cases of “picking” suggest the possibility of other diagnoses, including renal or hepatic failure, occult cancer, or other skin disease (eg, mastocytosis).
TAKE-HOME LEARNING POINTS
• Prurigo nodularis (PN) often presents with multiple papules, nodules, and/or plaques that develop primarily as a result of picking, rubbing, or scratching the area.
• PN patients appear to have a lowered threshold for itching, which may play a role in their disease.
• The differential for PN includes squamous cell carcinoma, psoriasis, atypical mycobacteria infection, and metastatic cancer.
• Biopsy plays a key role in establishing the correct diagnosis.
• Intralesional steroid injection with 10 mg/cc triamcinolone stops the itching and shrinks the lesion.