• A benign skin-limited disorder that overlaps with other entities, including dermal lupus erythematosus, cutaneous lymphoid hyperplasia, and polymorphic light eruption (PMLE).

• Males = females; onset typically during middle age; very rare in children.

• Most commonly appears on the head, neck, and upper back as one or several asymptomatic, erythematous papules, plaques (often annular) > nodules (Fig. 99.1); no secondary or surface changes (such as scale or crust).

• May last several weeks to months and will typically resolve spontaneously over months to years without sequelae.

• No systemic manifestations.

• DDx: see Fig. 99.2.

• Rx: watch-and-wait approach is often acceptable; if Rx desired, consider topical (class I) or intralesional CS; less often hydroxychloroquine is used.

• A benign, reactive lymphocytic proliferation that is thought to represent an exaggerated local immunologic reaction to a trigger that is usually unidentified.

• Females > males; adults > children.

• Inciting agents that have been reported include arthropod bites, tattoos, vaccinations, medications (e.g. antihistamines, antidepressants, angiotensin II receptor blockers), and in Europe, Borrelia burgdorferi infection.

• Presents most often on the head, neck, and upper extremities as one or several firm, erythematous to violaceous papules, plaques, or nodules (Fig. 99.3); usually no surface changes.

• Often spontaneously resolves without scarring.

• DDx (see Fig. 99.2): lymphocytic infiltrate of Jessner, lymphoma cutis, leukemia cutis, solid organ metastases, and occasionally adnexal tumors.

• Rx: topical (class I) or intralesional CS.

• Most commonly seen in neonates secondary to underlying bone marrow dysfunction; rarely in adults secondary to myelofibrosis, other myeloproliferative disorders or after splenectomy.

• Most often associated with TORCH (toxoplasmosis, other [e.g. parvovirus B19], rubella, cytomegalovirus) infections in neonates.

• Clinically presents with erythematous to violaceous papules and nodules > plaques, ulcers, or nasal polyps (Fig. 99.4).