What is the next step to confirm the diagnosis of skin lesions with bilateral hilar adenopathy on CXR?

Skin Biopsy to Confirm Sarcoidosis

The most appropriate next step is to perform a skin biopsy of the leg lesions to demonstrate noncaseating granulomas and confirm the diagnosis of sarcoidosis. 1

Clinical Presentation Strongly Suggests Sarcoidosis

This patient presents with the classic triad of sarcoidosis:

• Erythema nodosum (bilateral rounded, maculopapular, red and hot lesions over the extensor areas of the legs) 1
• Bilateral hilar adenopathy on chest X-ray 1
• Normal laboratory values excluding other systemic diseases 1

This constellation of findings, particularly erythema nodosum with bilateral hilar adenopathy, is highly suggestive of Löfgren's syndrome, a specific acute presentation of sarcoidosis that carries an excellent prognosis. 1, 2

Why Skin Biopsy is the Definitive Next Step

Diagnostic Confirmation Requirements

According to the American Thoracic Society guidelines, sarcoidosis diagnosis requires: 1

• Compatible clinical and radiologic findings
• Histologic evidence of noncaseating epithelioid granulomas
• Exclusion of other granulomatous diseases

Skin Lesions Provide Accessible Tissue

• The bilateral leg lesions represent easily accessible sites for biopsy without the risks associated with transbronchial or mediastinal lymph node sampling 1, 3
• Skin biopsy can be performed as an outpatient procedure with minimal morbidity 4
• The biopsy should demonstrate compact, tightly formed collections of epithelioid histiocytes and multinucleated giant cells characteristic of sarcoidosis 1

Histopathologic Features to Confirm

The pathologist should identify: 1

• Noncaseating granulomas (nonnecrotic or minimal ischemic necrosis)
• Perilymphatic distribution pattern
• Absence of infectious organisms on special stains
• Exclusion of other granulomatous conditions

Alternative Diagnostic Approaches (Less Preferred)

While Löfgren's syndrome can sometimes be diagnosed clinically without biopsy when the classic triad is present, tissue confirmation is strongly recommended to: 1

• Exclude malignancy (lymphoma can present similarly)
• Rule out infectious causes of granulomatous disease
• Confirm the diagnosis before initiating immunosuppressive therapy

Bronchoscopy with transbronchial biopsy would be an alternative if skin lesions were not present or accessible, but carries higher procedural risks including pneumothorax. 1

Mediastinal lymph node biopsy (via mediastinoscopy or EBUS) is unnecessary when accessible skin lesions are available for sampling. 1

Critical Pitfalls to Avoid

• Do not assume Löfgren's syndrome without tissue confirmation unless the clinical presentation is absolutely classic and the patient refuses biopsy 1
• Ensure special stains are performed to exclude mycobacterial and fungal infections that can mimic sarcoidosis 1
• Biopsy technique matters: A punch biopsy extending into the subcutaneous tissue is preferred over superficial shave biopsy to capture the full granulomatous architecture 4