# Systemic Sclerosis - Limited and Diffuse

## Introduction

Systemic sclerosis is an autoimmune connective tissue disease characterized by the triad of fibrosis, vasculopathy, and immune dysregulation affecting virtually every organ system. The disease is classified into two major subtypes, limited cutaneous systemic sclerosis and diffuse cutaneous systemic sclerosis, each with distinct clinical trajectories, autoantibody profiles, and patterns of organ involvement. Systemic sclerosis carries the highest mortality of any autoimmune rheumatic disease, and interstitial lung disease has surpassed scleroderma renal crisis as the leading cause of SSc-related death in the modern era.

## Classification and Subtypes

### Limited Cutaneous SSc (lcSSc)

Limited cutaneous systemic sclerosis is defined by skin thickening confined to the distal extremities, specifically the fingers, hands, and forearms below the elbows, and the face. This subtype was formerly known as CREST syndrome, an acronym encompassing calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia. A hallmark of lcSSc is that Raynaud phenomenon often precedes other disease features by years to decades, providing a prolonged window during which the diagnosis may be suspected but not yet confirmed. Anticentromere antibodies are positive in approximately 60 percent of patients with lcSSc. Pulmonary arterial hypertension is the major feared complication, occurring in 10 to 15 percent of patients, and the disease generally follows a slower progression compared to the diffuse subtype.

### Diffuse Cutaneous SSc (dcSSc)

Diffuse cutaneous systemic sclerosis is characterized by skin thickening that extends proximal to the elbows and knees and involves the trunk. The onset is typically more rapid, with skin changes developing within one year of the onset of Raynaud phenomenon. Anti-Scl-70, also known as anti-topoisomerase I, is positive in approximately 30 to 40 percent of patients with dcSSc. Anti-RNA polymerase III is positive in approximately 20 percent and carries distinctive clinical associations, including an elevated risk of scleroderma renal crisis and a temporal association with malignancy that warrants cancer screening. The diffuse subtype carries a higher risk of interstitial lung disease, cardiac involvement, and renal crisis compared to the limited form. Skin thickening characteristically peaks at 3 to 5 years and may then improve spontaneously, but visceral disease typically persists or progresses independently of skin softening.

### SSc sine scleroderma

SSc sine scleroderma represents a rare variant, accounting for approximately 5 percent of cases, in which patients develop visceral organ involvement consistent with systemic sclerosis without any skin thickening. Diagnosis rests on the identification of SSc-specific antibodies combined with internal organ involvement, Raynaud phenomenon, and characteristic nailfold capillaroscopy changes.

### 2013 ACR/EULAR Classification Criteria

The 2013 ACR/EULAR classification criteria employ a weighted scoring system in which a total score of 9 or greater classifies a patient as having systemic sclerosis. Skin thickening of the fingers extending proximal to the metacarpophalangeal joints is sufficient alone, scoring 9 points. Other items contributing to the score include puffy fingers (2 points), sclerodactyly (4 points), fingertip lesions including digital ulcers (2 points) or pitting scars (3 points), telangiectasia (2 points), abnormal nailfold capillaries (2 points), pulmonary arterial hypertension and/or interstitial lung disease (2 points), Raynaud phenomenon (3 points), and SSc-related antibodies (3 points).

<image>A comparison diagram of limited vs diffuse cutaneous systemic sclerosis shown on two human body outlines (anterior view). On the limited SSc figure, shade the areas of skin involvement in light blue: fingers, hands, forearms below the elbows, and face. On the diffuse SSc figure, shade in darker blue: fingers, hands, arms above and below elbows, trunk, and face. Next to each figure, list the key features: lcSSc (anticentromere antibody, PAH risk, slower progression, CREST features) and dcSSc (anti-Scl-70 or anti-RNA pol III, ILD risk, renal crisis risk, rapid progression). Include a timeline at bottom showing typical disease course for each subtype.</image>

## Autoantibody Profiles and Clinical Associations

### SSc-Specific Antibodies

The autoantibody profile in systemic sclerosis is remarkably predictive of clinical phenotype and prognosis. Anticentromere antibodies are associated with limited cutaneous disease, pulmonary arterial hypertension, and less frequent interstitial lung disease, conferring a relatively better prognosis overall. Anti-Scl-70, or anti-topoisomerase I, is associated with diffuse cutaneous disease and interstitial lung disease affecting 60 to 80 percent of positive patients, as well as digital ulcers, and confers a worse prognosis. Anti-RNA polymerase III is associated with diffuse cutaneous disease and carries a particularly notable 25 to 33 percent risk of scleroderma renal crisis; furthermore, the temporal association between anti-RNA polymerase III positivity and malignancy mandates cancer screening at the time of SSc diagnosis. Anti-U3 RNP, also known as anti-fibrillarin, is associated with diffuse cutaneous disease, pulmonary arterial hypertension, myositis, and is more prevalent in Black patients. Anti-Th/To is associated with limited cutaneous disease, interstitial lung disease, and pulmonary arterial hypertension, with a tendency toward later age of onset. Anti-PM-Scl defines an overlap phenotype with inflammatory myositis and is associated with mechanic's hands and interstitial lung disease.

| Antibody | SSc Subtype | ILD Risk | PAH Risk | Renal Crisis Risk | Cancer Association | Key Clinical Feature |
|----------|-----------|---------|---------|-------------------|-------------------|---------------------|
| Anticentromere (ACA) | Limited (lcSSc) | Low | **10–15%** | Low | No | CREST features; better prognosis |
| Anti-Scl-70 (anti-topoisomerase I) | Diffuse (dcSSc) | **60–80%** | Low | Low | No | ILD is the major threat; digital ulcers |
| Anti-RNA polymerase III | Diffuse (dcSSc) | Low | Low | **25–33%** | **Yes** (temporal cancer association) | Screen for renal crisis AND malignancy |
| Anti-U3 RNP (anti-fibrillarin) | Diffuse (dcSSc) | Moderate | Moderate | Low | No | More prevalent in Black patients; myositis |
| Anti-Th/To | Limited (lcSSc) | Moderate | Moderate | Low | No | Later age of onset |
| Anti-PM-Scl | Overlap (SSc-myositis) | Moderate | Low | Low | No | Mechanic's hands; inflammatory myopathy overlap |

### Non-specific Antibodies

Antinuclear antibodies are positive in more than 90 percent of patients with systemic sclerosis, with nucleolar and centromere immunofluorescence patterns being the most common. Anti-U1 RNP antibodies, when present, suggest overlap features with mixed connective tissue disease.

## Organ Involvement and Management

### Raynaud's Phenomenon

Raynaud phenomenon is present in more than 95 percent of patients with systemic sclerosis and is frequently the first manifestation of the disease. The classic triphasic color change involves white discoloration from vasospasm, followed by blue discoloration from cyanosis, and finally red discoloration during reperfusion. Digital ulcers occur in 30 to 50 percent of patients with diffuse cutaneous disease and cause significant morbidity including pain, infection, and functional limitation.

Management begins with lifestyle modifications including rigorous cold avoidance, smoking cessation, and use of warm gloves. First-line pharmacotherapy consists of dihydropyridine calcium channel blockers, with nifedipine at 30 to 60 milligrams daily or amlodipine at 5 to 10 milligrams daily being the most commonly used agents. Second-line therapies include phosphodiesterase-5 inhibitors such as sildenafil at 20 milligrams three times daily and topical nitroglycerin. For digital ulcers specifically, intravenous iloprost is effective but not available in the United States, while bosentan was shown in the RAPIDS-2 trial to reduce the development of new digital ulcers but did not heal existing ones. For refractory Raynaud phenomenon and digital ischemia, botulinum toxin injection into the digital neurovascular bundle and digital sympathectomy are therapeutic options.

### Interstitial Lung Disease

Interstitial lung disease is the leading cause of death in systemic sclerosis and has a prevalence of 40 to 75 percent in diffuse cutaneous disease and 25 to 35 percent in limited cutaneous disease. The nonspecific interstitial pneumonia pattern is the most common histologic pattern, accounting for approximately 77 percent of cases, with usual interstitial pneumonia being less common at approximately 11 percent. Screening requires pulmonary function tests measuring forced vital capacity and diffusing capacity for carbon monoxide at baseline and every 6 to 12 months, along with high-resolution CT of the chest. Disease extent is staged using the Goh staging system, in which disease extent greater than 20 percent on HRCT or FVC less than 70 percent predicted defines extensive disease warranting treatment.

The treatment landscape for SSc-ILD has expanded substantially. Mycophenolate mofetil is considered first-line therapy based on the SLS-II trial, which demonstrated that mycophenolate at 3 grams daily for 2 years was comparable in efficacy to oral cyclophosphamide given for 1 year followed by placebo for 1 year, with significantly better tolerability. Cyclophosphamide remains an option for progressive disease, supported by the SLS-I trial showing improved FVC at 12 months compared to placebo, though the effect waned after discontinuation. Nintedanib, an anti-fibrotic tyrosine kinase inhibitor, was demonstrated in the SENSCIS trial to reduce the annual rate of FVC decline by 44 milliliters per year compared to placebo and is approved for SSc-ILD at a dose of 150 milligrams twice daily. Tocilizumab at 162 milligrams subcutaneously weekly demonstrated preservation of FVC in early diffuse cutaneous SSc with elevated acute phase reactants in the focuSSced trial and has received FDA approval for SSc-ILD. Rituximab showed improvement in FVC in SSc-ILD in the Japanese DESIRES trial, and larger trials are ongoing. Lung transplantation is an option for end-stage ILD, with outcomes comparable to those for other ILD indications.

### Pulmonary Arterial Hypertension

Pulmonary arterial hypertension occurs in 8 to 12 percent of patients with systemic sclerosis, with a higher prevalence in limited cutaneous disease and anticentromere antibody-positive patients. Screening involves annual echocardiography combined with pulmonary function testing, with a pattern of declining DLCO with preserved FVC being a red flag for developing PAH. The DETECT algorithm provides a multi-step screening approach incorporating biomarkers such as NT-proBNP and urate levels, pulmonary function tests, ECG, and echocardiography to identify patients requiring right heart catheterization. Definitive diagnosis requires right heart catheterization demonstrating a mean pulmonary arterial pressure greater than 20 mmHg, a pulmonary arterial wedge pressure of 15 mmHg or less, and a pulmonary vascular resistance of 2 Wood units or greater, according to the 6th World Symposium on Pulmonary Hypertension definition.

Treatment follows established PAH guidelines and is similar to that for idiopathic PAH. Combination therapy with an endothelin receptor antagonist such as ambrisentan or macitentan plus a phosphodiesterase-5 inhibitor such as tadalafil or sildenafil, or alternatively a soluble guanylate cyclase stimulator such as riociguat, forms the cornerstone of management. The AMBITION trial demonstrated the superiority of upfront combination therapy with ambrisentan and tadalafil over monotherapy. The prostacyclin pathway provides additional therapeutic options including epoprostenol administered intravenously as the most potent agent, treprostinil available in subcutaneous, intravenous, inhaled, and oral formulations, and selexipag as an oral IP receptor agonist. Importantly, SSc-PAH carries a worse prognosis than idiopathic PAH.

### Scleroderma Renal Crisis

Scleroderma renal crisis occurs in 5 to 10 percent of patients with diffuse cutaneous disease, typically within the first 4 years of disease onset. Risk factors include anti-RNA polymerase III antibodies, diffuse cutaneous disease, glucocorticoid use at doses exceeding 15 milligrams of prednisone daily, and rapid skin progression. The classic presentation is abrupt-onset malignant hypertension with acute kidney injury, microangiopathic hemolytic anemia manifesting as schistocytes on peripheral smear, and thrombocytopenia. Normotensive renal crisis accounts for approximately 10 percent of cases; therefore, schistocytes and creatinine should be monitored even in the absence of hypertension.

The treatment of scleroderma renal crisis centers on ACE inhibitors, which are critical and potentially life-saving. Captopril is the preferred agent due to its short-acting, titratable pharmacokinetics, initiated at 6.25 to 12.5 milligrams and titrated every 8 to 12 hours to the maximum tolerated dose. The goal is to normalize blood pressure over 72 hours, avoiding overly rapid correction. ACE inhibitors should be continued even if the patient becomes dialysis-dependent, as approximately 50 percent of patients recover renal function over 12 to 24 months. Prophylactic ACE inhibitors have no role in SSc, as they may mask the early signs of renal crisis. Angiotensin receptor blockers should be avoided because the evidence supporting their use is insufficient compared to ACE inhibitors.

<image>A multi-panel organ involvement diagram for systemic sclerosis. Show a central human body figure with arrows pointing to affected organ systems, each with a detailed panel: (1) Lungs: ILD (NSIP pattern on HRCT with ground-glass opacities and subpleural reticulation) and PAH (enlarged pulmonary arteries, RV dilation). (2) Heart: Myocardial fibrosis, pericardial effusion, conduction abnormalities. (3) Kidneys: Renal crisis with TMA showing onion-skin lesion in interlobular artery. (4) GI tract: Esophageal dysmotility with dilated esophagus, gastric antral vascular ectasia (GAVE/watermelon stomach), small bowel pseudo-obstruction. (5) Skin: Sclerodactyly with digital ulcers, calcinosis. (6) Nailfold capillaroscopy: Show early (dilated capillaries), active (giant capillaries, hemorrhages), and late (avascular areas, bushy capillaries) SSc patterns. Label all findings clearly.</image>

### Gastrointestinal Involvement

Gastrointestinal involvement is the most common visceral manifestation of systemic sclerosis, affecting approximately 90 percent of patients. Esophageal dysmotility, characterized by reduced lower esophageal sphincter pressure and absent distal peristalsis, leads to severe gastroesophageal reflux disease. Management includes high-dose proton pump inhibitor therapy, prokinetic agents such as metoclopramide and erythromycin, and lifestyle modifications. Gastric antral vascular ectasia, also known as watermelon stomach, causes iron deficiency anemia from chronic gastrointestinal blood loss and is treated with endoscopic laser ablation or argon plasma coagulation. Small intestinal bacterial overgrowth results from impaired intestinal motility and presents with bloating, diarrhea, and malabsorption; diagnosis is typically made by glucose hydrogen breath test, and treatment involves empiric rotating antibiotics including rifaximin, metronidazole, and ciprofloxacin. Colonic pseudo-obstruction presents as colonic dilation without mechanical obstruction and is managed conservatively.

### Cardiac Involvement

Cardiac involvement in systemic sclerosis includes myocardial fibrosis occurring in a patchy distribution that can cause diastolic dysfunction and arrhythmias, pericardial effusions that are usually small but portend a poor prognosis when large, and conduction abnormalities including heart block and bundle branch block. Screening involves ECG and echocardiography, with cardiac MRI utilizing late gadolinium enhancement reserved for selected patients with suspected myocardial involvement.

### Musculoskeletal

Musculoskeletal manifestations include arthralgia and non-erosive arthritis, with tendon friction rubs being pathognomonic for diffuse cutaneous SSc and predictive of internal organ involvement. Myopathy is usually mild with mildly elevated creatine kinase, though overlap with inflammatory myopathy is possible. Calcinosis, consisting of subcutaneous calcium deposits, is painful, carries a risk of secondary infection, and has limited treatment options including colchicine, minocycline, and surgical excision for symptomatic lesions.

## Disease-Modifying Approaches

### Immunosuppressive Therapy

Methotrexate has demonstrated improvement in the modified Rodnan skin score in early diffuse cutaneous SSc in small randomized controlled trials. Mycophenolate mofetil has emerged as the first-line agent for SSc-ILD based on the SLS-II trial and is also used for skin disease. Cyclophosphamide, supported by SLS-I data, is now generally reserved for progressive ILD when other agents have failed. Tocilizumab, approved for SSc-ILD based on the focuSSced trial, may also benefit skin manifestations in early inflammatory diffuse cutaneous disease. Rituximab shows emerging evidence for improvement in both skin and lung disease, as demonstrated in the DESIRES trial. Nintedanib serves as an anti-fibrotic agent approved for SSc-ILD based on the SENSCIS trial.

### Autologous Hematopoietic Stem Cell Transplant (AHSCT)

Autologous hematopoietic stem cell transplantation represents the most aggressive therapeutic option for severe, early diffuse cutaneous systemic sclerosis. The ASTIS trial demonstrated that AHSCT was superior to intravenous cyclophosphamide for event-free survival at 4 years, achieving 79 percent versus 50 percent, despite a higher treatment-related mortality in the first year. The SCOT trial further confirmed that myeloablative AHSCT was superior to cyclophosphamide for event-free survival at 54 months. Patient selection is critical: candidates should have early diffuse cutaneous disease of less than 4 years duration with progressive skin or organ involvement and adequate cardiac and pulmonary reserve. Treatment-related mortality ranges from 3 to 10 percent, necessitating performance at specialized transplant centers with expertise in this procedure.

## Key Clinical Pearls

- Anti-RNA polymerase III antibodies should trigger screening for scleroderma renal crisis AND malignancy
- Glucocorticoids >15 mg/day are a risk factor for scleroderma renal crisis; avoid when possible
- Prophylactic ACE inhibitors do NOT prevent renal crisis and may mask early signs
- A declining DLCO with preserved FVC should prompt PAH screening with right heart catheterization
- Tendon friction rubs on physical exam are pathognomonic for dcSSc and predict poor prognosis
- MMF has largely replaced cyclophosphamide as first-line for SSc-ILD based on SLS-II tolerability data

## References
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2. Tashkin DP, et al. Mycophenolate mofetil versus oral cyclophosphamide in scleroderma-related interstitial lung disease (SLS-II). Lancet Respir Med. 2016;4(9):708-719.
3. Distler O, et al. Nintedanib for systemic sclerosis-associated interstitial lung disease (SENSCIS). N Engl J Med. 2019;380(26):2518-2528.
4. Sullivan KM, et al. Myeloablative autologous stem-cell transplantation for severe scleroderma (SCOT). N Engl J Med. 2018;378(1):35-47.
5. Khanna D, et al. Tocilizumab in systemic sclerosis (focuSSced). Lancet Respir Med. 2020;8(10):963-974.