Dermatology Flashcards

A 58-year-old woman presents with a pruritic, violaceous, flat-topped papule on her flexor wrist for 3 months. Biopsy shows a band-like lymphocytic infiltrate at the dermoepidermal junction with sawtooth rete ridges and Civatte bodies. She recently started hydrochlorothiazide 6 months ago. Which finding would most strongly support a lichenoid drug reaction over idiopathic lichen planus?

Answer: Presence of eosinophils within the dermal infiltrate

Lichenoid drug eruptions (LDE) mimic lichen planus histologically but characteristically show eosinophils and plasma cells in the dermal infiltrate, parakeratosis, and less prominent Civatte bodies compared to true LP. Eosinophils within the band-like infiltrate is the hallmark distinguishing feature. Mucous membrane involvement, IgM deposits at the DEJ (cytoid bodies), and Wickham's striae can occur in both idiopathic LP and LDE.

A 34-year-old man with HIV (CD4 count 85 cells/µL) presents with rapidly enlarging, tender, vascular nodules on the legs and a concurrent papular eruption on the trunk. Bacillary angiomatosis is suspected. Which organism is responsible, and what is the treatment of choice?

Answer: Bartonella henselae or B. quintana; erythromycin or doxycycline

Bacillary angiomatosis is caused by Bartonella henselae (cat-scratch exposure) or B. quintana (body louse exposure) in immunocompromised patients, particularly those with HIV and low CD4 counts. It presents as vascular proliferations that clinically resemble Kaposi sarcoma. Biopsy shows lobular vascular proliferation with clumps of granular material (bacteria visible on Warthin-Starry stain). First-line treatment is erythromycin 500 mg QID or doxycycline 100 mg BID for at least 3 months to prevent relapse.

A 72-year-old woman on long-term hydroxyurea for polycythemia vera develops painful leg ulcers on the medial malleoli and hyperpigmented, atrophic skin. She also has megaloblastic changes on CBC and dermatomyositis-like changes on her hands. What is the most likely diagnosis explaining her cutaneous findings?

Answer: Hydroxyurea-induced dermatomyositis-like syndrome with leg ulcers

Long-term hydroxyurea use is associated with a well-recognized cutaneous toxicity syndrome including painful leg ulcers (typically medial malleolar), dermatomyositis-like changes (Gottron-like papules over knuckles, poikiloderma), nail changes, and xerosis. This occurs due to hydroxyurea's antiproliferative effects on keratinocytes and impaired wound healing. Unlike true dermatomyositis, muscle enzymes and EMG are normal. Treatment requires dose reduction or discontinuation of hydroxyurea.

A 45-year-old woman presents with recurrent episodes of painful, erythematous nodules on her shins that resolve with bruise-like hyperpigmentation over 2–6 weeks. A biopsy from the center of a fresh lesion shows a septal panniculitis without vasculitis. Workup reveals elevated ACE levels and bilateral hilar adenopathy on chest X-ray. What is the most appropriate next step in management?

Answer: Reassurance and NSAIDs; no systemic treatment needed for this benign, self-limited manifestation

This presentation describes Löfgren syndrome — the triad of erythema nodosum, bilateral hilar lymphadenopathy, and periarthritis/arthritis, which is an acute presentation of sarcoidosis. Erythema nodosum in Löfgren syndrome is a reactive, immunologically mediated phenomenon, not true cutaneous sarcoidosis. It carries an excellent prognosis with >90% spontaneous resolution within 2 years. NSAIDs and rest are first-line; systemic corticosteroids are not routinely indicated for this benign variant. Biopsy of erythema nodosum in this context is not diagnostic of sarcoidosis (it shows nonspecific septal panniculitis).

A 29-year-old woman presents with grouped, tense vesicles on erythematous skin over the elbows, knees, and buttocks. Direct immunofluorescence of perilesional skin shows granular IgA deposits at the dermal papillae. She has mild iron deficiency anemia. Which HLA type is most strongly associated with her condition, and what is the critical dietary counseling point?

Answer: HLA-DQ2 and HLA-DQ8; strict lifelong gluten-free diet to prevent enteropathy-associated T-cell lymphoma

This is dermatitis herpetiformis (DH), pathognomonic by granular IgA at dermal papillae on DIF. DH is the cutaneous manifestation of gluten-sensitive enteropathy (celiac disease) and is strongly associated with HLA-DQ2 (>90%) and HLA-DQ8. The underlying gluten-sensitive enteropathy carries a risk of enteropathy-associated T-cell lymphoma (EATL) if untreated. A strict lifelong gluten-free diet is the cornerstone of treatment, as it treats both the skin and intestinal disease and reduces lymphoma risk. Dapsone controls the skin eruption but does not treat the underlying enteropathy or reduce lymphoma risk.

A 55-year-old man presents with a slowly growing, flesh-colored plaque on his cheek with overlying telangiectasias and a pearly border. Dermoscopy reveals arborizing vessels and shiny white-pink ovoid nests. He asks about Mohs micrographic surgery versus standard excision. Which subtype of this tumor has the highest rate of perineural invasion and subclinical spread, making Mohs most critically indicated?

Answer: Morpheaform (sclerosing) basal cell carcinoma

Morpheaform (sclerosing) BCC is the most aggressive subtype, characterized by strands of basaloid cells embedded in a dense fibrous stroma. It presents as an indurated, scar-like plaque and has indistinct clinical margins. It has the highest rates of subclinical tumor extension, perineural invasion, and recurrence after standard excision. Mohs micrographic surgery is particularly critical for morpheaform BCC because its infiltrative growth pattern makes clinical margin assessment unreliable, and frozen section margin control during Mohs ensures complete excision. Nodular and superficial BCCs have more predictable margins and lower perineural invasion rates.