Residency · Residency · Dermatology

Granulomatous Dermatoses: Sarcoidosis, Granuloma Annulare, and Beyond

Overview

Granulomatous dermatoses are a group of conditions characterized by the formation of granulomas in the skin. Granulomas are organized collections of activated macrophages (epithelioid histiocytes), often accompanied by multinucleated giant cells and surrounded by lymphocytes. The differential diagnosis is broad, spanning infectious, inflammatory, and foreign body etiologies, and recognizing the specific granuloma type in its clinical context is essential for accurate diagnosis.

Granuloma Classification

Granulomas are classified by their histologic architecture. The sarcoidal (naked) granuloma consists of tight epithelioid granulomas with minimal surrounding lymphocytes, as seen in sarcoidosis. The tuberculoid granuloma features epithelioid granulomas with caseating necrosis, characteristic of tuberculosis and atypical mycobacterial infections. Palisading granulomas demonstrate histiocytes arranged around a central zone of degenerated collagen or mucin, as found in granuloma annulare and necrobiosis lipoidica. Suppurative granulomas contain central neutrophilic abscesses within granulomatous tissue, typical of deep fungal infections, atypical mycobacteria, and ruptured cysts or follicles. Foreign body granulomas show multinucleated giant cells containing intracytoplasmic foreign material, caused by suture, silicone, tattoo pigment, or other exogenous substances.

Cutaneous Sarcoidosis

Epidemiology

Sarcoidosis is a multisystem granulomatous disease of unknown etiology, with higher prevalence and severity in African Americans at a ratio of approximately 3:1 compared to Caucasians. Peak age of onset is between 25 and 35 years. Skin involvement occurs in 25 to 35 percent of sarcoidosis patients and may be the presenting sign.

Pathogenesis

The disease is driven by an exaggerated Th1/Th17 immune response to unknown antigens in genetically susceptible individuals. CD4+ T cells and macrophages drive granuloma formation, with TNF-alpha playing a critical role in granuloma maintenance. Possible environmental triggers include mycobacterial antigens, propionibacteria, and inorganic particles.

Clinical Manifestations

Sarcoidosis is often called the "great imitator" in dermatology because it can mimic virtually any skin condition. The most common presentation is papular or nodular disease, with red-brown to violaceous papules and nodules on the face, trunk, and extremities. Plaque-type sarcoidosis produces indurated plaques with predilection for the face, scalp, and trunk. Annular sarcoidosis presents as ring-shaped plaques, classically on the face. Lupus pernio is one of the most characteristic forms, appearing as indurated violaceous plaques on the nose, cheeks, and ears and carrying a strong association with chronic pulmonary sarcoidosis and upper respiratory tract involvement. Subcutaneous sarcoidosis (Darier-Roussy) manifests as firm, non-tender subcutaneous nodules. Erythema nodosum is associated with acute sarcoidosis, particularly in Lofgren syndrome, but notably is not itself a granulomatous lesion histologically. Scar sarcoidosis, in which granulomas infiltrate old scars, is a highly characteristic finding. Additional presentations include ichthyosiform, psoriasiform, lichenoid, morpheaform, verrucous variants, and scarring alopecia from scalp granulomas.

Lofgren Syndrome

Lofgren syndrome is a form of acute sarcoidosis defined by the triad of bilateral hilar lymphadenopathy, erythema nodosum, and polyarthralgias. It carries an excellent prognosis and is usually self-limited, occurring more commonly in Scandinavian and Irish populations.

Diagnosis

Biopsy reveals non-caseating ("naked") granulomas with minimal surrounding lymphocytic infiltrate. Asteroid bodies and Schaumann bodies within giant cells may be seen but are non-specific. Special stains (GMS, PAS, Fite) and tissue cultures to exclude infection are mandatory whenever non-caseating granulomas are found. Polarized light examination should be performed to exclude foreign body reactions.

Systemic Workup for Cutaneous Sarcoidosis

The workup for cutaneous sarcoidosis includes chest X-ray or CT chest (bilateral hilar lymphadenopathy is present in approximately 90 percent), pulmonary function tests, CBC and CMP with attention to calcium and liver function, ACE level (elevated in approximately 60 percent but neither sensitive nor specific), 24-hour urine calcium (hypercalciuria from granulomatous 1-alpha hydroxylase activity), ophthalmologic examination for uveitis, and ECG with or without cardiac MRI for cardiac sarcoidosis screening.

Treatment

Limited cutaneous disease is treated with topical or intralesional corticosteroids. Moderate-to-severe skin or systemic disease requires systemic therapy, with options including hydroxychloroquine or chloroquine, methotrexate (the most commonly used steroid-sparing agent), tetracyclines such as minocycline or doxycycline for mild skin disease, TNF-alpha inhibitors (infliximab, adalimumab) for refractory cases, apremilast (with emerging evidence for cutaneous sarcoidosis), and systemic corticosteroids as bridging therapy for severe disease.

Granuloma Annulare (GA)

Epidemiology

Granuloma annulare is common and often self-limited, with peak incidence in children and young adults. There is a female predominance of approximately 2:1. A possible association with diabetes mellitus has been debated, particularly in the generalized variant.

Pathogenesis

The etiology is unknown, with proposed mechanisms including delayed-type hypersensitivity, vasculitis or microangiopathy leading to collagen degeneration, and Th1-mediated immune responses with macrophage activation. Reported triggers include trauma, insect bites, sun exposure, infections, and drugs.

Clinical Variants

Localized GA is the most common variant, presenting as ring-shaped (annular) plaques with central clearing on the dorsal hands and feet, elbows, and knees, and is often self-limited within two years. Generalized GA produces widespread papules and annular plaques on the trunk and extremities, tends to be more persistent, and may warrant diabetes screening. Subcutaneous GA (deep GA) manifests as firm, painless subcutaneous nodules, is common in children on the scalp, pretibial area, and hands, and can mimic a rheumatoid nodule. Perforating GA presents as papules with central umbilication and transepidermal elimination of degenerated collagen, typically on the dorsal hands. Patch or macular GA appears as erythematous or brown patches without a palpable annular border. Interstitial GA is histologically subtle, displaying a "busy dermis" pattern with interstitial histiocytes between collagen bundles.

Histopathology

The hallmark is a palisading granuloma surrounding a central zone of degenerated collagen and mucin, which stains positively with Alcian blue or colloidal iron. The interstitial variant shows histiocytes dissecting between collagen bundles without a well-formed palisade. Importantly, there is no necrobiosis, as opposed to necrobiosis lipoidica. Necrobiosis lipoidica shows tiered granulomas spanning the full dermis with necrobiosis, while rheumatoid nodules show central fibrinoid necrosis in a deeper, subcutaneous location.

Treatment

Observation is often appropriate for localized GA, as approximately 50 percent of cases resolve spontaneously within two years. Topical and intralesional corticosteroids are first-line for localized disease. Phototherapy (NB-UVB or PUVA) is used for generalized GA. Systemic options for generalized or refractory disease include hydroxychloroquine, dapsone, methotrexate, TNF-alpha inhibitors, and JAK inhibitors (with emerging reports of efficacy). Isotretinoin and pentoxifylline have only anecdotal evidence.

Necrobiosis Lipoidica (NL)

Clinical Features

Necrobiosis lipoidica presents as well-defined, yellow-brown atrophic plaques on the pretibial area, with central waxy, atrophic, telangiectatic skin surrounded by a violaceous active border. Ulceration occurs in approximately 30 percent of cases. NL is associated with diabetes mellitus in approximately 60 to 70 percent of patients, although only 0.3 percent of diabetics develop NL. The condition is bilateral in roughly 80 percent of cases.

Histopathology

The histologic hallmark is tiered (layered) granulomatous inflammation spanning the full dermis and subcutis, with palisading granulomas alternating with zones of necrobiosis (degenerated collagen). Plasma cells are often present, serving as a distinguishing feature from GA. Vascular wall thickening and endothelial swelling are additional findings.

Treatment

Necrobiosis lipoidica is notoriously difficult to treat, with no consistently effective therapy. Options include topical and intralesional corticosteroids (used cautiously to avoid further atrophy in already thin skin), topical tacrolimus, pentoxifylline, aspirin with dipyridamole, and TNF-alpha inhibitors for refractory disease. Wound care is essential for ulcerated lesions. Notably, glycemic control does not reliably improve NL.

Foreign Body Granulomas

Foreign body granulomas are caused by exogenous or endogenous foreign material in the dermis. Common exogenous causes include suture, silicone, paraffin, tattoo pigment, wood splinters, and insect parts. Endogenous causes include ruptured cyst contents, hair shaft (pilonidal), and urate crystals in gout. Histology shows multinucleated giant cells with intracytoplasmic foreign material, which may be polarizable under polarized light. Silicone granulomas display a characteristic "Swiss cheese" pattern with clear spaces surrounded by histiocytes. Treatment involves removing the foreign body when possible, intralesional corticosteroids, and surgical excision.

Other Granulomatous Conditions

Granulomatous rosacea presents as papules and nodules on the face with non-caseating granulomas and must be differentiated from lupus miliaris disseminatus faciei. Interstitial granulomatous dermatitis is associated with autoimmune disease and drugs, presenting as linear cords (the "rope sign") or plaques. Interstitial granulomatous drug reaction produces palisading granulomas in association with medications including colchicine, calcium channel blockers, and ACE inhibitors. Crohn disease can produce cutaneous granulomas in perianal fissures and fistulae, as well as metastatic Crohn disease with granulomas at distant skin sites. Granulomatous slack skin is a rare variant of cutaneous T-cell lymphoma with granulomas and skin laxity.

<image>Clinical photograph panel showing: (A) cutaneous sarcoidosis with red-brown papules and plaques on the face, (B) lupus pernio showing violaceous indurated plaques on the nose, (C) localized granuloma annulare with annular plaque and central clearing on the dorsal hand, (D) necrobiosis lipoidica showing yellow-brown atrophic plaque with telangiectasia on the pretibial area. Include diverse skin tones.</image>

<image>Histopathology comparison diagram showing three granuloma patterns side by side: (A) sarcoidal (naked) non-caseating granulomas of sarcoidosis with minimal lymphocytic rim, (B) palisading granuloma of granuloma annulare with central mucin deposition and peripheral histiocytes, (C) foreign body granuloma with multinucleated giant cells containing polarizable foreign material. Label each pattern clearly with key distinguishing features.</image>

<image>Flowchart for the diagnostic approach to granulomatous dermatitis: starting with skin biopsy showing granulomas, branching based on granuloma type (sarcoidal, palisading, suppurative, foreign body), required special stains and cultures, and leading to specific diagnoses. Include decision points for systemic workup (chest imaging, serology, ophthalmology referral) when sarcoidosis is suspected.</image>

Key Clinical Pearls

Sarcoidosis can mimic virtually any dermatosis, so it should always be considered in the differential of unexplained papules, plaques, or nodules, especially in African American patients. Scar sarcoidosis, in which granulomas infiltrate old scars, is a highly characteristic finding, and suspicious scar changes should always be biopsied. Special stains and tissue cultures for mycobacteria and fungi are mandatory when non-caseating granulomas are found, as infection must be excluded before diagnosing sarcoidosis. Lupus pernio (violaceous plaques on the nose and cheeks) predicts chronic pulmonary fibrosis and upper airway involvement, and these patients require aggressive systemic treatment. Granuloma annulare is often self-limited, and overtreatment should be avoided; patient education and watchful waiting are appropriate for localized disease. The association between generalized GA and diabetes mellitus is inconsistent; obtaining a fasting glucose or HbA1c is reasonable, but an extensive diabetes workup is not mandatory.

References

• Haimovic A, Sanchez M, Engel JM, Grinspan D. Sarcoidosis: a comprehensive review and update for the dermatologist. J Am Acad Dermatol. 2012;66(5):699-718.
• Piette EW, Rosenbach M. Granuloma annulare: clinical and histologic variants, hypothesis of pathogenesis, and treatment. Int J Dermatol. 2016;55(8):837-847.
• Reid SD, Ladizinski B, Lee K, Baber A, Adams A. Update on necrobiosis lipoidica: a review of etiology, diagnosis, and treatment options. J Am Acad Dermatol. 2013;69(5):783-791.
• Wanat KA, Rosenbach M. A practical approach to cutaneous sarcoidosis. Am J Clin Dermatol. 2014;15(4):283-297.

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