A 72-year-old woman who spends summers in rural Germany presents with a progressive rash on her left leg pictured below.

It has been present for over a year. She experiences some occasional tingling/burning but otherwise has no systemic symptoms. A skin biopsy shows a thinned epidermis, sparse perivascular and interstitial lymphoplasmacytic infiltrate in the dermis, and a loss of elastic fibers.

Which of the following is the most likely diagnosis?

A. Livedoid vasculopathy
B. Lichen sclerosus
C. Necrobiosis lipoidica
D. Acrodermatitis chronica atrophicans
E. Cutaneous T-cell lymphoma

Rationale: 

This patient’s chronic, violaceous, atrophic plaques with visible vasculature on the distal leg, combined with histologic findings and a history of potential tick exposure in Europe are classic for acrodermatitis chronica atrophicans (ACA). ACA is a late cutaneous manifestation of Lyme borreliosis which is most commonly caused by Borrelia afzelii and almost exclusively seen in Europe. It can persist for months to years and progresses through inflammatory and atrophic stages, resulting in the thin, parchment-like skin and telangiectasia characteristic of end-stage disease.

Correct answer: D. Acrodermatitis chronica atrophicans

ACA develops insidiously and often begins with bluish-red discoloration and swelling, progressing to marked epidermal and dermal atrophy. Neuropathic symptoms such as paresthesias and dysesthesias may occur due to perineural inflammation. The biopsy findings of epidermal thinning, lymphoplasmacytic infiltrate, and elastic fiber loss are supportive. Serology typically shows positive IgG to Borrelia, especially B. afzelii. Early recognition is important, as oral doxycycline or IV ceftriaxone may arrest progression if started in earlier stages.

Incorrect answer choices:

A. Livedoid vasculopathy typically presents with painful ulcerations, porcelain-white scars (atrophie blanche), and thrombosis of dermal vessels, not with smooth atrophy and visible veins. Histology would show fibrin thrombi and minimal inflammation which are absent in this vignette. 

B. Lichen sclerosus may cause atrophy and whitening, but it typically affects genital areas, with homogenized collagen and vacuolar interface change on histology. ACA presents with a more violaceous hue and a different distribution.

C. Necrobiosis lipoidica usually presents with yellow-brown, atrophic plaques with telangiectasias on the shins, often in diabetic patients. Histology would reveal layered granulomas and necrobiosis not the lymphoplasmacytic infiltrate seen in ACA.

E. Cutaneous T-cell lymphoma (CTCL) presents with patches and plaques, often in non–sun-exposed sites, and shows epidermotropism of atypical lymphocytes on biopsy. The histology and slow involvement in this patient are not consistent with CTCL.

Additional reading at Fitzpatrick's Dermatology Chapter 179: Lyme Borreliosis