Residency · Residency · Rheumatology

Sarcoidosis - Rheumatologic Manifestations

Introduction

Sarcoidosis is a multisystem granulomatous disease of unknown etiology that affects the lungs, lymph nodes, skin, eyes, and joints, among other organ systems. Its prevalence in the United States is approximately 10 to 20 per 100,000, with a three-fold higher incidence in African Americans; Scandinavian populations also carry elevated risk. The peak age of onset is between 25 and 45 years, with a bimodal distribution in some populations. Rheumatologic manifestations are common, occurring in 25 to 40 percent of patients, and can be the presenting feature that prompts initial medical evaluation. The histopathologic hallmark of sarcoidosis is the non-caseating granuloma, a finding that distinguishes it from other granulomatous diseases, particularly tuberculosis.

Pathogenesis

The pathogenesis of sarcoidosis involves an exaggerated granulomatous immune response to an as-yet-unidentified antigen or antigens, driven by Th1 and Th17 lymphocyte pathways. Macrophage activation leads to granuloma formation and the production of pro-inflammatory cytokines including TNF-alpha, IFN-gamma, IL-12, and IL-17. Within the granulomas, CD4-positive T cells with a Th1 predominant phenotype are abundant, while peripheral blood typically shows lymphopenia due to T cell sequestration in affected organs. Genetic susceptibility is conferred by multiple HLA and non-HLA loci, with HLA-DRB103:01 associated with acute disease and Lofgren syndrome, and HLA-DRB114 and *15 associated with chronic disease. Additional susceptibility genes include BTNL2 and ANXA11. Environmental factors implicated in sarcoidosis include mycobacterial antigens (particularly mKatG), Propionibacterium acnes, and occupational exposures such as beryllium, which produces berylliosis as a clinical mimic. A distinctive feature of sarcoidosis pathophysiology is the expression of 1-alpha-hydroxylase by granuloma macrophages, which drives extrarenal production of calcitriol (1,25-dihydroxyvitamin D), leading to hypercalcemia and hypercalciuria.

Musculoskeletal Manifestations

Acute Sarcoid Arthritis (Lofgren Syndrome)

Lofgren syndrome is the classic acute presentation of sarcoidosis, defined by the triad of bilateral hilar lymphadenopathy, erythema nodosum, and polyarthralgia or polyarthritis. The most characteristic joint finding is periarticular ankle inflammation, manifesting as bilateral ankle swelling, erythema, and tenderness. This is often periarticular in nature (periarthritis) rather than true intra-articular synovitis, a distinction that is important for accurate characterization. The presentation is acute and self-limited, resolving in weeks to months in most patients. The prognosis is excellent, with more than 90 percent of patients achieving complete resolution without chronic sequelae. HLA-DRB1*03:01 is associated with Lofgren syndrome and independently predicts a favorable outcome. Treatment consists of NSAIDs as first-line therapy, with low-dose glucocorticoids reserved for inadequate responses; further therapy is rarely necessary.

Chronic Sarcoid Arthritis

Chronic sarcoid arthritis is defined as persistent or recurrent polyarthritis lasting more than 6 months. It can closely mimic rheumatoid arthritis, presenting as symmetric polyarthritis affecting the wrists, metacarpophalangeal joints, proximal interphalangeal joints, knees, and ankles. The arthritis is usually non-erosive, although erosive sarcoid arthritis has been reported. Chronic sarcoid arthritis is typically associated with chronic multisystem sarcoidosis involving the lungs, skin, and eyes. HLA-DRB114 and 15 are associated with this chronic phenotype. Distinguishing chronic sarcoid arthritis from rheumatoid arthritis requires recognition that rheumatoid factor and anti-CCP are typically negative and that synovial biopsy reveals non-caseating granulomas rather than the pannus formation characteristic of RA.

Dactylitis

Sarcoid dactylitis produces "sausage digits" through granulomatous tenosynovitis and soft tissue infiltration. Radiographs may demonstrate lytic bone lesions in the form of phalangeal cysts. Dactylitis may present as an isolated finding in sarcoidosis. The differential diagnosis includes psoriatic arthritis, spondyloarthritis, tuberculous dactylitis, and sickle cell disease.

Osseous Sarcoidosis

Bone involvement occurs in 3 to 13 percent of sarcoidosis patients. The hands and feet are most commonly affected, demonstrating a characteristic lace-like lytic pattern in the phalanges on radiographs. The axial skeleton can also be affected, with vertebral lesions that mimic metastatic disease on imaging. Osseous sarcoidosis is frequently asymptomatic and discovered incidentally. Skull involvement is rare but has been described. PET-CT is useful for identifying FDG-avid bone lesions and for staging the extent of skeletal involvement.

Sarcoid Myopathy

Sarcoid myopathy presents in three distinct patterns. Chronic myopathy is the most common form, manifesting as progressive proximal weakness that mimics polymyositis, with mild CK elevation. Nodular myopathy presents with palpable muscle nodules representing mass-forming granulomas. Acute myositis is rare and presents with severe weakness and significant CK elevation. Diagnosis requires muscle biopsy demonstrating non-caseating granulomas. Treatment consists of glucocorticoids with or without steroid-sparing agents such as methotrexate or azathioprine.

<image>A comprehensive illustration of rheumatologic manifestations of sarcoidosis. Show a patient figure with labeled arrows to: (1) Ankles: Bilateral periarticular ankle swelling and erythema (Lofgren syndrome), with inset showing erythema nodosum on the shins as tender, erythematous subcutaneous nodules. (2) Hands: Dactylitis of a finger with underlying lytic bone lesion, and an X-ray inset showing "lace-like" lytic pattern in the phalanges (cystic bone changes). (3) Lungs: CXR showing bilateral hilar lymphadenopathy (stage II sarcoidosis). (4) Skin: Lupus pernio (violaceous, indurated plaques on the nose and cheeks). (5) Eyes: Anterior uveitis with keratic precipitates on slit-lamp exam. (6) Muscle: Cross-section showing non-caseating granuloma with multinucleated giant cells, epithelioid macrophages, and surrounding lymphocytic cuff (no central necrosis). Include a box listing Lofgren syndrome triad: BHL + erythema nodosum + polyarthralgia.</image>

Other Organ Manifestations Relevant to Rheumatology

Pulmonary Sarcoidosis (Staging)

Pulmonary sarcoidosis is classified according to a radiographic staging system based on chest radiograph findings. Stage 0 represents a normal chest radiograph. Stage I is defined by bilateral hilar lymphadenopathy alone. Stage II consists of bilateral hilar lymphadenopathy with pulmonary infiltrates. Stage III demonstrates pulmonary infiltrates without hilar lymphadenopathy. Stage IV represents established pulmonary fibrosis. Stages I and II frequently self-resolve, while Stage IV fibrosis is irreversible, underscoring the importance of early recognition and treatment to prevent progression.

Cutaneous

Cutaneous manifestations of sarcoidosis are diverse. Erythema nodosum presents as painful subcutaneous nodules on the anterior shins and represents a reactive inflammatory process rather than granulomatous infiltration; importantly, it should not be biopsied to diagnose sarcoidosis. Lupus pernio consists of violaceous, indurated plaques on the nose, cheeks, and ears and is a marker of chronic sarcoidosis associated with upper airway involvement and osseous lesions. Papules, plaques, and nodules elsewhere on the skin contain non-caseating granulomas histologically. Scar sarcoidosis, in which granulomas infiltrate old scars, is a distinctive manifestation.

Ocular (25-50%)

Ocular involvement occurs in 25 to 50 percent of sarcoidosis patients. Anterior uveitis is the most common ocular manifestation, characterized by "mutton-fat" keratic precipitates reflecting its granulomatous nature. Posterior uveitis produces "candle-wax drippings" (retinal periphlebitis). Lacrimal gland enlargement can mimic IgG4-related disease or Sjogren syndrome. Annual ophthalmologic screening is recommended for all sarcoidosis patients.

Calcium Metabolism

Hypercalcemia occurs in 10 to 20 percent of sarcoidosis patients, resulting from extrarenal production of 1,25-dihydroxyvitamin D by macrophages within granulomas expressing 1-alpha-hydroxylase. Hypercalciuria is more common than hypercalcemia, affecting 40 to 60 percent of patients, and can lead to nephrolithiasis and nephrocalcinosis. Glucocorticoids effectively suppress 1-alpha-hydroxylase activity and correct the calcium abnormality. Excessive vitamin D supplementation and sun exposure should be avoided in sarcoidosis patients. Calcium levels should be monitored regularly.

Neurologic (5-10%)

Neurologic involvement occurs in 5 to 10 percent of sarcoidosis patients. Cranial neuropathy is the most common neurologic manifestation, with cranial nerve VII (facial nerve palsy) most frequently affected. Bilateral facial nerve palsy in the context of parotid gland enlargement, uveitis, and fever constitutes Heerfordt syndrome. Central nervous system involvement includes hypothalamic and pituitary disease, which may cause diabetes insipidus or hypopituitarism, and leptomeningeal disease. Small fiber neuropathy is common, affecting approximately 40 percent of patients, while large fiber neuropathy is less frequent. Treatment of neurosarcoidosis requires glucocorticoids combined with steroid-sparing agents, with methotrexate, mycophenolate mofetil, or infliximab used for refractory cases.

Cardiac (5% clinical; 25% subclinical on autopsy)

Cardiac sarcoidosis is clinically evident in approximately 5 percent of patients but is found in up to 25 percent at autopsy, indicating significant underdiagnosis. Conduction abnormalities, particularly atrioventricular block, are the most common cardiac manifestation, and bundle branch block may also occur. Granulomatous myocardial infiltration can produce dilated or restrictive cardiomyopathy. Ventricular arrhythmias carry a risk of sudden cardiac death. Screening should include baseline and annual electrocardiography, echocardiography, cardiac MRI with late gadolinium enhancement for identifying fibrosis, and PET-CT for detecting active inflammation. Treatment involves glucocorticoids, implantable cardioverter-defibrillator placement for arrhythmia risk, and pacemaker insertion for high-degree AV block.

Diagnosis

Laboratory

Serum angiotensin-converting enzyme is elevated in 40 to 60 percent of sarcoidosis patients but lacks specificity, as it is elevated in many granulomatous diseases. Lysozyme is less specific than ACE. Calcium levels, both total and ionized, should be checked, along with 24-hour urine calcium. Complete blood count may reveal lymphopenia due to CD4-positive T cell sequestration in tissues, and anemia of chronic disease may be present. ESR and CRP are mildly elevated in active disease. Hypergammaglobulinemia with a polyclonal pattern is common. Elevated alkaline phosphatase suggests hepatic granulomas. Both 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D should be measured, with the latter typically elevated due to extrarenal production.

Histopathology (Required for Diagnosis)

Histopathologic confirmation is required for the diagnosis of sarcoidosis, with the single exception of Lofgren syndrome, which can be diagnosed clinically when the classic triad is present. The characteristic finding is compact, well-formed non-caseating granulomas composed of epithelioid histiocytes and multinucleated giant cells, which may be of the Langhans or foreign-body type. Schaumann bodies (laminated calcifications) and asteroid bodies may be found within giant cells but are not specific for sarcoidosis. The absence of caseation is the critical feature distinguishing sarcoidosis from tuberculosis, and special stains for acid-fast bacilli and fungi must be negative. Biopsy may be obtained from lymph nodes, skin lesions, lung (via transbronchial biopsy), salivary glands, or liver, depending on clinical accessibility and involvement.

Imaging

Chest radiography is the first-line imaging study and forms the basis of the pulmonary staging system. High-resolution CT of the chest may reveal ground-glass opacities, nodules with a characteristic perilymphatic distribution, and fibrosis. PET-CT identifies active granulomatous inflammation through FDG avidity and is useful for identifying biopsy sites, assessing disease extent, monitoring treatment response, and evaluating cardiac sarcoidosis. MRI is the preferred modality for evaluating neurosarcoidosis and cardiac involvement.

Management

General Principles

Not all sarcoidosis requires treatment, as many patients, particularly those with Lofgren syndrome and Stage I pulmonary disease, experience spontaneous remission. Indications for treatment include progressive pulmonary disease, cardiac involvement, central nervous system involvement, severe ocular disease, hypercalcemia, progressive organ dysfunction, and symptomatic musculoskeletal disease. The overarching treatment goal is organ preservation and prevention of irreversible fibrosis.

Pharmacotherapy

Glucocorticoids are the first-line therapy for most organ manifestations. For pulmonary sarcoidosis, prednisone at 20 to 40 mg daily is administered for 4 to 6 weeks before tapering over 6 to 12 months. Cardiac and CNS involvement require higher doses, typically prednisone at 40 to 60 mg daily or intravenous methylprednisolone for acute presentations. Musculoskeletal disease is initially managed with NSAIDs for acute arthritis, with glucocorticoids reserved for chronic or refractory cases.

Methotrexate at 10 to 25 mg weekly is the first-line steroid-sparing agent, with evidence supporting its use in skin, joint, and pulmonary sarcoidosis. The METHOSAR trial has provided supporting data for pulmonary sarcoidosis. Azathioprine at 2 mg/kg daily is an alternative steroid-sparing option. Mycophenolate mofetil is used for renal involvement, pulmonary disease, and neurosarcoidosis. Hydroxychloroquine is effective for skin disease, arthralgia, and hypercalcemia but is not adequate for pulmonary sarcoidosis. Leflunomide serves as an alternative for skin and joint manifestations.

Among biologic agents, infliximab is the most extensively studied and is effective for refractory pulmonary sarcoidosis, cutaneous disease including lupus pernio, neurosarcoidosis, and cardiac sarcoidosis. A critically important distinction is that etanercept is not effective for sarcoidosis and may paradoxically worsen the disease, making infliximab the biologic of choice. Adalimumab is an alternative anti-TNF option. Rituximab has been reported in case series for refractory sarcoidosis but evidence remains limited. JAK inhibitors, particularly tofacitinib, have shown promise in early reports for refractory disease.

<image>A treatment algorithm for sarcoidosis organized by organ system involvement. Central decision node: "Sarcoidosis confirmed by biopsy (non-caseating granulomas, AFB/fungal stains negative)." Branch to organ-specific pathways. Lofgren syndrome → NSAIDs → observation (excellent prognosis, >90% resolve). Chronic arthritis/musculoskeletal → NSAIDs → HCQ → MTX → GC → infliximab. Pulmonary (progressive) → GC 20-40 mg → taper with MTX or AZA → infliximab if refractory. Cardiac → GC 40-60 mg + ICD if arrhythmia risk → MTX/AZA → infliximab. Neurosarcoidosis → GC (high-dose) → MTX/MMF → infliximab. Skin (lupus pernio) → topical GC → HCQ → MTX → infliximab. Hypercalcemia → GC (rapid response) → HCQ. Include a note: "Etanercept is NOT effective and may worsen sarcoidosis."</image>

Key Clinical Pearls

• Lofgren syndrome (BHL + erythema nodosum + polyarthralgia) has excellent prognosis; biopsy often unnecessary if classic triad present
• Erythema nodosum is NOT granulomatous; it is a septal panniculitis and should not be biopsied to diagnose sarcoidosis
• Etanercept is ineffective and may paradoxically worsen sarcoidosis; infliximab is the biologic of choice
• Hypercalcemia in sarcoidosis is due to extrarenal 1,25-dihydroxyvitamin D production; avoid vitamin D supplementation
• Cardiac sarcoidosis is underdiagnosed; screen all patients with baseline ECG; cardiac MRI and PET for high-risk features
• Small fiber neuropathy is common (~40%) and underrecognized in sarcoidosis; consider if neuropathic pain present

References

1. Crouser ED, 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, et al. ERS clinical practice guidelines on treatment of sarcoidosis. Eur Respir J. 2021;58(6):2004079.
3. Sweiss NJ, et al. Rheumatologic manifestations of sarcoidosis. Semin Respir Crit Care Med. 2010;31(4):463-473.
4. Judson MA. The diagnosis of sarcoidosis: attempting to apply rigor to arbitrary and unrigorous concepts. Chest. 2018;154(5):1006-1007.
5. Baughman RP, et al. Infliximab therapy in patients with chronic sarcoidosis and pulmonary involvement. Am J Respir Crit Care Med. 2006;174(7):795-802.

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