Scratching the Surface of the Problem

ANSWER

The least likely diagnosis is staph infection (choice “b”). By their very nature, staph infections are suppurative, often involving redness, swelling, pain, and purulent drainage. They can be chronic (eg, MRSA) but are more typically of acute onset. And they usually resolve on their own or with treatment; recall that this patient was treated for staph infection many times without any change.

She was also treated repeatedly for scabies (choice “a”), a condition that could certainly last 15 years. However, the lack of improvement with treatment, combined with the absence of suggestive signs, make this diagnosis improbable.

Mycosis fungoides (MF; choice “c”) is a type of T-cell lymphoma that often develops with itching and plaque formation over the course of years. It was ultimately ruled out by the biopsy results (as were scabies and staph infection).

What the biopsy did show was epidermal thickening—a characteristic sign of prurigo nodularis (choice “d”).

DISCUSSION

Prurigo nodularis is a localized form of neurodermatitis caused by picking and scratching. As with the classic form, the more the patient scratches, the more the lesions itch and multiply. In this case, biopsy of the larger plaque showed hypertrophic scarring.

The patient’s skin-picking habit likely developed during (and perhaps because of) her methamphetamine use. Long-term exposure to the itch-scratch-itch cycle can make treatment problematic. In this case, a class 4 topical steroid cream was prescribed, along with injection of several larger lesions with 10 mg/mL triamcinolone suspension.

It’s worth mentioning that for patients with this type of history, general lab testing (ie, complete blood count and complete metabolic panel) should be performed to rule out organic disease and other serious conditions (eg, renal or hepatic failure, leukemia). Fortunately, this patient’s results were reassuring on that front.