A linear purpuric rash in an elderly man

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Case presentation

An 88-year-old male presented to the dermatology clinic for evaluation of a rash on his left thigh. This rash had been present for several months and was asymptomatic. His primary care physician diagnosed the rash as atopic dermatitis; however, there was no improvement with emollients or triamcinolone 0.1% cream. He denied a history of herpes zoster and had received the shingles vaccine. On physical exam, there were red-brown papules coalescing into plaques in a linear distribution across his left thigh (Fig 1). A punch biopsy showed band-like lymphocytic infiltrate at the dermal-epidermal junction, along with erythrocyte extravasation and hemosiderin deposition (Fig 2).Fig 1. Fig 2

Question 1: what is the diagnosis?

• A.Linear lichenoid pigmented purpura
• B.Lichen striatus
• C.Linear lichen planus
• D.Linear Darier disease
• E.Linear psoriasis

Answers:

• A.Linear lichenoid pigmented purpura – Correct. Pigmented purpuric dermatosis (PPD) describes a group of chronic skin disorders characterized by distinct red-to-golden brown macules, patches, and papules with petechiae.1^,^2 PPD is generally divided into 55 major variants, with linear pigmented purpura – also known as unilateral linear capillaritis – being a rarer form. It often presents unilaterally on an extremity, sometimes in a blaschkoid distribution such as in our patient.1^,^3^,^4 On histology, lymphocytic inflammation with extravasated erythrocytes in the upper dermis is seen.1^,^4 Our patient’s histology was consistent with a lichenoid pattern, helping further classify the diagnosis as the even more rare linear lichenoid pigmented purpura.4
• B.Lichen striatus – Incorrect. Lichen striatus primarily occurs in children, and skin biopsy shows peri-eccrine lymphocytic inflammation.4
• C.Linear lichen planus – Incorrect. Linear lichen planus presents with significant pruritus, deep purple-colored lesions, and postinflammatory hyperpigmentation.4 In addition, histology shows a lichenoid band of inflammation in the papillary dermis with epidermal hyperplasia and hypergranulosis but without extravasated erythrocytes.4
• D.Linear Darier disease – Incorrect. Segmental Darier disease is typically composed of keratotic, sometimes crusted, papules that are pink to red-brown rather than purpuric. Histopathologic findings include acantholysis and dyskeratosis.
• E.Linear psoriasis – Incorrect. Linear psoriasis typically presents as intensely pruritic, erythematous, and scaly papules and plaques along Blaschko’s lines. Biopsy would not show a lichenoid infiltrate.5

Question 2: which is the most common underlying cause of this condition?

• A.Hepatitis C
• B.Medication-induced
• C.Liver disease
• D.Genetic mosaicism
• E.Idiopathic

Answers:

• A.Hepatitis C – Incorrect. Hepatitis C is associated with the development of lichen planus.
• B.Medication-induced – Incorrect. Although medications are frequently reported as triggers for PPD, the etiology of PPD is unknown.1 Identified medication triggers include acetaminophen, aspirin, chlordiazepoxide, glipizide, and hydralazine.1^,^2^,^4
• C.Liver disease – Incorrect. PPD is rarely associated with systemic disorders such as hyperlipidemia, diabetes mellitus, rheumatoid arthritis, thyroid disease, liver disease, and hematologic or solid neoplasms.2
• D.Genetic mosaicism – Incorrect. Genetic mosaicism is believed to play a role in the pathogenesis of linear psoriasis, although the exact mechanism is not completely understood.5
• E.Idiopathic – Correct. Most cases of PPD are idiopathic. PPD results from minimal inflammation and hemorrhage of vessels of the superficial dermis, most commonly capillaries, in the absence of coagulopathy.2^,^3 Physical activity, prolonged standing, venous hypertension, capillary fragility, and local infections are underlying factors that may lead to the development or worsen preexisting PPD.2

Question 3: what other variants of this entity can also present with lichenoid inflammation on histopathology?

• A.Lichen aureus
• B.Pigmented purpuric lichenoid dermatitis of Gougerot and Blum
• C.Purpura annularis telangiectodes of Majocchi
• D.A & B
• E.A, B, & C

Answers:

• A.Lichen aureus – Incorrect. Although lichen aureus does have a lichenoid infiltrate, this is not the only variant of PPD that may show the lichenoid pattern.2^,^4
• B.Pigmented purpuric lichenoid dermatitis of Gougerot and Blum – Incorrect. Similar to lichen aureus, pigmented purpuric lichenoid dermatitis of Gougerot and Blum may also have a lichenoid infiltrate.2^,^4
• C.Purpura annularis telangiectodes of Majocchi – Incorrect. Purpura annularis telangiectodes of Majocchi does not typically have a lichenoid infiltrate, but rather a perivascular pattern of lymphocytic inflammation, which is similar to Schamberg disease.2
• D.A & B – Correct. Both of those variants exhibit a lichenoid inflammatory pattern.3
• E.A, B, & C – Incorrect. See explanation for answer choice C.3

Conflicts of interest

None disclosed.