Residency · Residency · Respirology

Sarcoidosis

Epidemiology and Pathogenesis

Epidemiology

Sarcoidosis demonstrates dramatic variation in prevalence by race and geography, with rates ranging from 35-80 per 100,000 in Black Americans to 10-15 per 100,000 in White Americans, and with the highest global prevalence observed in Scandinavian countries. The disease follows a bimodal age distribution, with the primary peak occurring between ages 25-35 and a second peak between ages 45-65, particularly in women. Black patients are more likely to develop severe, chronic, and extrapulmonary disease, including higher rates of cardiac and ocular involvement. Familial clustering is well documented, with 5-16% of patients having an affected first-degree relative, a finding confirmed by the ACCESS study.

Pathogenesis

The fundamental pathologic process in sarcoidosis is granulomatous inflammation triggered by an unknown antigen in genetically susceptible individuals. The characteristic lesion is the non-caseating granuloma, composed of organized aggregates of epithelioid macrophages, multinucleated giant cells, and CD4+ T lymphocytes. The immune response is dominated by Th1 and Th17 pathways, with elevated levels of IFN-gamma, TNF-alpha, IL-12, and IL-17. A paradoxical feature of sarcoidosis immunology is the coexistence of peripheral immune anergy, manifesting as cutaneous anergy to tuberculin and other recall antigens, with intense local immune activation at granulomatous sites. Proposed causative antigens include mycobacterial antigens such as mKatG and ESAT-6, Propionibacterium acnes, and the self-antigen vimentin, though none has been definitively established. Genetic associations include HLA-DRB10301, which is linked to Lofgren syndrome and a favorable prognosis, and HLA-DRB11501, which is associated with chronic disease. BTNL2 polymorphisms have also been implicated in disease susceptibility.

Clinical Manifestations

Pulmonary (>90%)

Pulmonary involvement occurs in more than 90% of sarcoidosis patients. Bilateral hilar lymphadenopathy (BHL) is the most common radiographic finding. Parenchymal infiltrates manifest as perilymphatic nodules, ground glass opacity, or consolidation. Fibrotic sarcoidosis, occurring in 5-10% of patients, produces upper-lobe fibrosis with traction bronchiectasis and volume loss. Airway involvement includes endobronchial granulomas visible as mucosal cobblestoning on bronchoscopy, and may progress to airway stenosis. Pulmonary hypertension in sarcoidosis is multifactorial, resulting from fibrosis, granulomatous vasculitis, extrinsic compression of pulmonary vessels by lymphadenopathy, and portopulmonary mechanisms.

Scadding Staging (Chest Radiograph)

The Scadding staging system classifies pulmonary sarcoidosis by chest radiograph appearance and carries important prognostic implications. Stage 0 indicates a normal chest radiograph with extrapulmonary disease only. Stage I shows bilateral hilar lymphadenopathy alone. Stage II demonstrates BHL accompanied by pulmonary infiltrates. Stage III shows pulmonary infiltrates without BHL. Stage IV represents irreversible pulmonary fibrosis. The prognostic significance of staging is substantial: Stage I disease undergoes spontaneous remission in 60-80% of cases, Stage II in 50-60%, Stage III in approximately 30%, and Stage IV rarely remits.

Extrapulmonary Manifestations

Skin involvement occurs in 25-35% of patients and spans a wide spectrum. Erythema nodosum carries an excellent prognosis and is a component of Lofgren syndrome. Lupus pernio, characterized by chronic purple-blue plaques on the nose and cheeks, indicates chronic disease requiring sustained treatment. Other cutaneous manifestations include papular and nodular lesions and scar sarcoidosis. Ocular involvement affects 25-50% of patients, with anterior uveitis being the most common manifestation, followed by posterior uveitis, lacrimal gland enlargement, and optic neuritis; all sarcoidosis patients require ophthalmologic evaluation. Liver involvement occurs in 20-30% of patients, manifesting as granulomatous hepatitis with usually subclinical elevation of alkaline phosphatase, though clinically significant liver disease is uncommon. Cardiac sarcoidosis is clinically apparent in approximately 5% of patients but is present subclinically in up to 25% at autopsy or advanced imaging studies. Manifestations include conduction abnormalities with atrioventricular block being the most common, cardiomyopathy, and sudden cardiac death. Screening with ECG is recommended for all patients, with cardiac MRI demonstrating late gadolinium enhancement or FDG-PET pursued when cardiac involvement is suspected, and implantable cardioverter-defibrillator placement considered for high-risk patients. Neurologic involvement affects 5-10% of patients, with cranial nerve palsies being the most common presentation, particularly facial nerve (CN VII) palsy which may be bilateral. Other neurologic manifestations include meningitis, hypothalamic and pituitary involvement, and small fiber neuropathy. Hypercalcemia and hypercalciuria occur in 10-20% of patients due to the presence of 1-alpha-hydroxylase within granulomas, which converts 25-hydroxyvitamin D to the active 1,25-dihydroxyvitamin D, potentially causing nephrolithiasis and nephrocalcinosis. Joint manifestations range from acute polyarthritis in Lofgren syndrome to chronic arthropathy. Hematologic findings include lymphopenia reflecting sequestration of T cells in granulomatous lesions, splenomegaly, and hypogammaglobulinemia.

Lofgren Syndrome

Lofgren syndrome is a distinct acute presentation comprising the classic triad of erythema nodosum, bilateral hilar lymphadenopathy, and polyarthralgia or arthritis. It carries an excellent prognosis with greater than 90% spontaneous resolution within two years. The presentation is sufficiently characteristic that biopsy confirmation is often not required when the clinical picture is classic. An association with HLA-DRB1*0301 has been established.

<image>A comprehensive organ involvement diagram for sarcoidosis showing a human body silhouette with labeled arrows pointing to affected organ systems. For each system, list the specific manifestations and approximate frequency: Lungs (>90% - BHL, infiltrates, fibrosis), Eyes (25-50% - uveitis, lacrimal gland), Skin (25-35% - erythema nodosum, lupus pernio), Liver (20-30% - granulomatous hepatitis), Heart (5-25% - AV block, cardiomyopathy), CNS (5-10% - cranial neuropathy, meningitis), Joints (arthralgia, Lofgren), Kidneys (hypercalcemia, nephrolithiasis), Spleen, Parotid glands (Heerfordt syndrome). Use color intensity to indicate frequency. Include insets showing histologic non-caseating granuloma with labeled epithelioid cells, giant cells, and Schaumann bodies.</image>

Diagnosis

Diagnostic Triad

The diagnosis of sarcoidosis rests on three pillars: a compatible clinical and radiologic presentation, histologic evidence of non-caseating granulomas, and exclusion of other granulomatous diseases including tuberculosis, non-tuberculous mycobacterial infection, fungal infection, berylliosis, foreign body granulomatosis, granulomatosis with polyangiitis, Crohn disease, and drug reactions.

Biopsy Sites and Techniques

The choice of biopsy site and technique depends on the clinical presentation and accessible disease sites. Endobronchial biopsy yields granulomas in 40-60% of cases even when the bronchial mucosa appears macroscopically normal. Transbronchial biopsy achieves a diagnostic yield of 50-70% in Stage I-II disease. Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) has emerged as the first-line technique for sampling mediastinal and hilar lymphadenopathy, with a yield of 80-90% as demonstrated in the GRANULOMA study. When accessible, biopsy of a peripheral lymph node, skin lesion, or other extrapulmonary site is preferred as the least invasive approach. Mediastinoscopy is rarely needed in the current era given the availability and high yield of EBUS.

Laboratory Findings

Serum angiotensin-converting enzyme (ACE) level is elevated in approximately 60% of sarcoidosis patients but has poor sensitivity and specificity, is not recommended for diagnosis, and has a limited role in monitoring, though some experts track trends over time. Soluble IL-2 receptor (sIL-2R) is more sensitive and specific than ACE and is increasingly recognized as a useful biomarker for both diagnosis and disease activity monitoring. Hypercalcemia should be assessed with serum calcium, though 24-hour urine calcium is a more sensitive measure. Elevated 1,25-dihydroxyvitamin D (calcitriol) reflects granuloma 1-alpha-hydroxylase activity. Lymphopenia results from T cell sequestration in granulomatous lesions. Elevated alkaline phosphatase suggests hepatic involvement. BAL findings include a CD4/CD8 ratio greater than 3.5, which is suggestive though not diagnostic, and lymphocytosis exceeding 15%.

Screening for Organ Involvement

All patients with newly diagnosed sarcoidosis should undergo comprehensive screening for organ involvement. Baseline investigations include a complete blood count, comprehensive metabolic panel with attention to calcium, renal function, and hepatic function, 24-hour urine calcium, ECG, ophthalmologic examination, and pulmonary function tests with spirometry and DLCO. Cardiac screening begins with a baseline ECG; abnormalities or symptoms such as conduction disturbances, palpitations, or syncope should prompt cardiac MRI and/or FDG-PET, with the important caveat that a 72-hour high-fat, low-carbohydrate diet is required before FDG-PET to suppress physiologic myocardial glucose uptake. Neurologic evaluation with brain MRI with contrast and cerebrospinal fluid analysis is pursued when symptoms suggest CNS involvement.

Management

When to Treat

A fundamental principle of sarcoidosis management is that not all patients require treatment, as many cases resolve spontaneously, particularly Stage I disease. Indications for treatment include progressive pulmonary disease with declining FVC or DLCO, symptomatic disease impairing quality of life, dangerous organ involvement encompassing cardiac, neurologic, and ocular disease (particularly posterior uveitis and optic neuritis), severe hypercalcemia, and progressive renal disease, as well as disfiguring lupus pernio. Asymptomatic bilateral hilar lymphadenopathy (Stage I) with preserved lung function should be observed rather than treated.

First-Line: Corticosteroids

Prednisone at 20-40 mg daily for 4-6 weeks followed by a gradual taper over 6-12 months represents first-line therapy. The total treatment duration for pulmonary disease is typically 12-24 months. Tapering too rapidly leads to relapse in 30-70% of patients, necessitating a slow and careful dose reduction. Lofgren syndrome should be managed initially with NSAIDs, reserving short-course corticosteroids for refractory cases.

Second-Line: Steroid-Sparing Agents

Methotrexate at 10-15 mg weekly with folate supplementation of 1-5 mg daily is the most commonly used steroid-sparing agent, with a response rate of approximately 60-70%. Monitoring includes regular CBC and liver function tests every 4-8 weeks, with awareness of the risks of hepatotoxicity, cytopenias, and teratogenicity. Azathioprine at 2 mg/kg daily, with TPMT enzyme activity checked before initiation, serves as an alternative to methotrexate. Mycophenolate mofetil at 1-1.5 g twice daily is increasingly used and may be better tolerated than methotrexate. Leflunomide at 10-20 mg daily has evidence primarily in cutaneous and pulmonary sarcoidosis. Hydroxychloroquine at 200-400 mg daily is particularly useful for skin disease, hypercalcemia, and fatigue, with monitoring for retinal toxicity through annual ophthalmologic examination recommended after 5 years of use.

Third-Line: Anti-TNF Therapy

Infliximab, administered at 3-5 mg/kg intravenously at weeks 0, 2, and 6, then every 4-8 weeks, has the strongest evidence base among TNF inhibitors for sarcoidosis. Its indications include refractory pulmonary, cardiac, neurologic, and cutaneous sarcoidosis. Screening for latent tuberculosis with IGRA or PPD testing, along with hepatitis B serologies, is mandatory before initiation. Adalimumab at 40 mg subcutaneously every 1-2 weeks serves as an alternative to infliximab. A critically important distinction is that etanercept is not effective in sarcoidosis, a mechanistic difference attributable to its inability to neutralize membrane-bound TNF, unlike infliximab and adalimumab.

Emerging Therapies

Several novel therapeutic approaches are under investigation. JAK inhibitors, including tofacitinib and baricitinib, have shown benefit in case reports and small series of refractory sarcoidosis. Repository corticotropin injection (Acthar Gel) is FDA-approved for sarcoidosis and possesses mechanisms beyond cortisol release through melanocortin receptor agonism. Anti-IL-12/23 therapy with ustekinumab has been evaluated in a phase 2 trial in chronic pulmonary sarcoidosis with modest benefit. Namilumab, an anti-GM-CSF antibody, is in early phase trials.

<image>A treatment algorithm for sarcoidosis management. Start with newly diagnosed sarcoidosis. First decision node: observation criteria met? (asymptomatic, Stage I, preserved PFTs, no dangerous organ involvement). If yes, observe with serial PFTs, imaging, and organ screening q3-6 months. If no (treatment indicated), start first-line prednisone 20-40 mg/day. Show taper schedule over 6-12 months. If steroid-dependent (relapse below prednisone 10 mg) or steroid-intolerant, add second-line agent (methotrexate, azathioprine, or mycophenolate). If refractory to second-line after 3-6 months, escalate to third-line anti-TNF therapy (infliximab). Include special boxes for organ-specific considerations: cardiac (ICD if indicated), neuro (high-dose IV steroids initially), ocular (topical + systemic), and hypercalcemia (hydroxychloroquine + steroids). Use color gradients from green (observe) to red (third-line) indicating treatment intensity.</image>

Monitoring and Prognosis

Monitoring

Disease activity monitoring includes pulmonary function tests with spirometry and DLCO every 3-6 months during active disease and annually when stable. Chest radiography or CT should be obtained periodically while avoiding excessive radiation exposure. Serum calcium and renal function should be monitored regularly. sIL-2R or ACE levels may be tracked for trends. Screening for treatment side effects includes glucose monitoring, bone density assessment, and ophthalmologic examinations for patients on hydroxychloroquine.

Prognosis

Approximately 50% of sarcoidosis patients achieve resolution within 2-3 years. Roughly 25% develop chronic persistent disease, and 5-10% progress to advanced fibrotic disease. Overall mortality ranges from 1-5%, with most deaths attributable to pulmonary fibrosis with respiratory failure or cardiac sarcoidosis presenting as sudden death. Poor prognostic factors include Black race, age greater than 40, lupus pernio, cardiac or neurologic involvement, Stage III or IV disease, and the requirement for chronic immunosuppression.

Key Clinical Pearls

• Not all sarcoidosis needs treatment; asymptomatic Stage I disease resolves spontaneously in 60-80% of cases and should be observed rather than treated
• Cardiac sarcoidosis may present as sudden death; screen all sarcoidosis patients with ECG; pursue cardiac MRI or FDG-PET if any conduction abnormality, palpitations, syncope, or unexplained cardiomyopathy
• Etanercept is NOT effective in sarcoidosis (unlike infliximab and adalimumab); this is due to its mechanism of action not neutralizing membrane-bound TNF
• Hypercalcemia in sarcoidosis is driven by granuloma 1-alpha-hydroxylase activity; avoid vitamin D supplementation unless 25-OH vitamin D is truly deficient AND calcium is closely monitored
• ACE level is neither sensitive nor specific enough for diagnosis or reliable monitoring of sarcoidosis; sIL-2R is a superior biomarker

References

1. Crouser ED, Maier LA, Wilson KC, et al. Diagnosis and Detection of Sarcoidosis: An Official American Thoracic Society Clinical Practice Guideline. Am J Respir Crit Care Med. 2020;201(8):e26-e51.
2. Baughman RP, Valeyre D, Korsten P, et al. ERS clinical practice guidelines on treatment of sarcoidosis. Eur Respir J. 2021;58(6):2004079.
3. Judson MA, Baughman RP, Costabel U, et al. Efficacy of infliximab in extrapulmonary sarcoidosis: results from a randomised trial. Eur Respir J. 2008;31(6):1189-1196.
4. Birnie DH, Sauer WH, Bogun F, et al. HRS expert consensus statement on the diagnosis and management of arrhythmias associated with cardiac sarcoidosis. Heart Rhythm. 2014;11(7):1305-1323.
5. Baughman RP, Culver DA, Judson MA. A concise review of pulmonary sarcoidosis. Am J Respir Crit Care Med. 2011;183(5):573-581.

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