Dusky plaque on the knee

Granuloma annulare is part of the differential

A wide range of diseases comprise the differential diagnosis of sarcoidosis. These diseases include:⁹

• Granuloma annulare. It is also a granulomatous skin disease, but it appears as single or multiple rings.
• Rheumatoid nodules. These usually appear in the context of a diagnosis of rheumatoid arthritis.
• Granulomatous mycosis fungoides. This type of cutaneous lymphoma has many clinical forms, including granuloma formation.
• Syringoma. On inspection, you’ll see small, firm adnexal benign tumors that usually appear around the upper cheeks and lower eyelids
• Xanthelasma. These are benign, yellow macules, papules, or plaques that tend to appear on the eyelids. Patients with xanthelasma often have a lipid disorder.
• Lichen planus. This is a very pruritic skin involvement with pink to violaceous papules and plaques. It may present in different locations, but the most common areas are the wrists and ankles.
• Granulomatous rosacea. This is a variant of rosacea characterized by uniform papules on the face.

Clinical findings, biopsy clinch the diagnosis

The diagnosis of sarcoidosis is made by a combination of clinical and histologic findings.¹

• Clinical findings. Cutaneous involvement is either “specific” or “nonspecific.”
• With specific cutaneous involvement, which our patient had, you’ll see typical noncaseating granulomas, with no evidence of infection or a foreign body. It may be disfiguring, but it’s almost always nontender and it is rarely ulcerative.
• With nonspecific cutaneous involvement, you’ll see erythema nodosum lesions, especially on the legs. The serum angiotensin-converting enzyme (ACE) level is elevated in many of these patients.