Sarcoidosis is a multi-system inflammatory condition characterized by the formation of tiny clumps of inflammatory cells, called granulomas, in various organs. The skin is the second most commonly affected organ after the lungs, with cutaneous involvement occurring in 20% to 35% of all sarcoidosis patients. The visual presentation of sarcoidosis on the skin is highly varied, earning it the nickname “the great mimicker” of dermatology. Skin symptoms can range from subtle bumps to large, disfiguring patches, and may even be the first sign of the disease before internal organs are affected.
Common Manifestations and Morphology
The most frequent forms of cutaneous sarcoidosis are distinct lesions that contain the characteristic sarcoidal granulomas. These specific lesions are often categorized by their size and shape, appearing as papules, plaques, or nodules. Papules are small, raised bumps that can be reddish-brown, violaceous, tan, or the same color as the surrounding skin. These bumps often appear in clusters, particularly around the eyes, on the neck, or in skin folds, and possess a firm, waxy texture.
Plaques are larger, flat-topped, elevated lesions that may be oval, annular (ring-shaped), or irregular in outline. Their color typically ranges from reddish-brown to purple, and they commonly affect the trunk, limbs, and buttocks. Plaques may present with a fine, subtle scale, or they may feel smooth or scaly to the touch.
Nodules represent deeper, firmer lesions that form beneath the surface of the skin. These are typically found on the extremities, such as the arms and legs, caused by granulomatous inflammation in the fat tissue under the skin. They are usually painless and are often described as lumps under the skin, rarely breaking down to form an open sore. Clinicians look for the “apple jelly” sign, where pressing a glass slide (diascopy) onto a reddish-brown lesion reveals a yellowish-brown, translucent color due to the underlying granulomas.
Distinctive Facial and Scar-Related Lesions
Lupus Pernio is one of the most recognizable forms of cutaneous sarcoidosis, often signaling a more chronic and severe course of the disease. It is characterized by indurated, violaceous or dusky red-purple plaques and nodules. Lupus Pernio lesions are specifically located on the central face, heavily involving the nose, cheeks, ears, and lips.
Lupus Pernio lesions have a hardened, almost woody texture and can progressively infiltrate the underlying cartilage and bone structure, potentially leading to disfigurement. This appearance is strongly associated with systemic involvement, particularly in the respiratory tract, and is generally more resistant to treatment than other skin sarcoidosis types. Even small papules on the nasal rim can indicate a risk of granulomatous infiltration of the nasal mucosa.
Sarcoidosis has a characteristic tendency to develop within areas of previous skin injury, known as scar sarcoidosis. Existing scars from trauma, surgery, or vaccinations can become infiltrated by sarcoidal granulomas. The scar tissue typically becomes raised, indurated, and changes color, often turning purple, reddish, or brownish. A similar reaction can occur within the pigment of old tattoos, where small bumps or plaques, frequently brown or black, form strictly within the tattooed area.
Atypical and Rare Skin Presentations
While papules, plaques, and Lupus Pernio are the most common specific manifestations, sarcoidosis can present in several less frequent and visually confusing ways. Hypopigmented sarcoidosis appears as patches of skin lighter than the surrounding skin, often observed in individuals with darker skin tones. Conversely, some lesions can break down the surface, resulting in open sores known as ulcerative sarcoidosis, though this is rare.
Other rare variants can visually mimic entirely different skin conditions, making diagnosis challenging. Psoriasiform sarcoidosis, for instance, presents as scaling plaques that strongly resemble common psoriasis. Similarly, ichthyosiform sarcoidosis causes a fish-scale appearance, typically on the lower legs, that mimics ichthyosis. These atypical forms confirm the disease’s reputation as a dermatologic imitator, often requiring a biopsy for proper identification.
It is important to distinguish specific sarcoidosis lesions from Erythema Nodosum (EN), which is a non-specific manifestation. EN presents as tender, warm, red to reddish-purple bumps, most commonly found on the shins. Erythema Nodosum is not a sarcoidal granuloma but an inflammatory reaction in the fat layer beneath the skin. Its appearance is often a sign of acute, self-limiting sarcoidosis, such as Löfgren syndrome.
Confirming the Diagnosis of Cutaneous Sarcoidosis
Due to the wide variety of visual presentations, relying on the appearance of the skin lesions alone is insufficient for a definitive diagnosis. Cutaneous sarcoidosis can look like many other conditions, including infections, granuloma annulare, lupus erythematosus, and various lymphomas, necessitating a medical professional to consider a broad differential diagnosis.
The definitive method for confirming cutaneous sarcoidosis is a skin biopsy, which is the gold standard. A small sample of the affected skin is examined under a microscope to identify the characteristic non-caseating granulomas. The presence of these specific collections of inflammatory cells provides the necessary histopathologic evidence to establish the diagnosis.
Once cutaneous sarcoidosis is confirmed via biopsy, a systemic evaluation is necessary because skin involvement often occurs alongside or precedes internal organ disease. This evaluation typically includes a physical examination and initial testing, such as a chest X-ray and an eye examination, to determine if the disease affects the lungs or eyes. Identifying skin sarcoidosis is an opportunity to check for asymptomatic disease in other parts of the body.