This patient has psychogenic itch, which is localized pruritus associated with a concomitant diagnosis (or symptoms of) depression, anxiety, or somatoform disorders. Self-reported depression is present in about 40% of persons with psychogenic pruritus. Most patients are able to identify a precipitating psychological trigger. Patients with psychogenic pruritus excessively pick and scratch normal skin and report constant pruritus. Physical examination findings include linear crusted lesions and hypopigmented scars. It is important to examine patients carefully and completely to avoid missing a dermatologic or systemic cause of itch in those with concomitant psychiatric disorders.

Morbilliform drug eruptions can be pruritic; however, this patient has only secondary skin changes (linear erosions) and does not have a primary finding that would be expected with a drug eruption.

Localized itching with less prominent skin lesions suggests neuropathic pruritus, which results from inflammation or damage to sensory nerves. The most common forms are notalgia paresthetica and brachioradial pruritus. With notalgia paresthetica, there is recurrent and persistent itching on the medial back, usually around the scapula. Brachioradial pruritus causes itching on the extensor forearms, arms, or upper back. The itch in these conditions is often described as burning or stinging, and some patients experience a crawling sensation. The skin is initially normal but may become excoriated, lichenified, and hyperpigmented from recurrent rubbing and scratching. Patients often obtain relief with application of ice, and this may be a distinguishing characteristic.

Patients with generalized pruritus who lack primary skin lesions may have an associated medical condition or internal malignancy. However, hematologic or hepatobiliary malignancies are more likely diagnoses than colorectal adenocarcinomas.