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Systemic Sclerosis



SSc 
  • dcSSc
  • lcSSc

Note: Scleroderma,  characterized by thick and endurated skin is a distinguishing hallmark of Six


Genetic factors: Loci similar to SLE, RA, Psoriasis suggesting common pathogenic pathways shared among these phenotypically dissimilar conditions.  
 (Harrison's)

Envioronmental and occupational risk factors:  (Harrison's)
  • Viral infections: Parvo Virus B19, CMV, EBV
  • Similar skin induration but varying biopsy findings. Conditions include. 
    • Toxic oil syndrome (contamination  rapeseed oil for cooking)
    • Eosinophilia Mayalgia Syndrome (l-tryptophan supplementation)
    • Nephrogenic Systemic Fibrosis linked to gadolinium 
  • Cigarette : Not linked (unlike RA)

Pathogenesis:  (Harrison's)
  • Sustained Fibroblast activation (Amplifying and Maintenance mechanisms B and C below)  is the key often initiated by transient generation of ROS and immune damage to the endothelial cells (triggering : A )





As noted above, sustained activation of Fibroblast is the key. Picture below highlights the mechanism of activation of fibroblasts. 
3 main pathways
  • SMAD signaling 
  • Non-smad signaling 
  • RAS-ERK1 signaling 



  • 3 cardinal pathophysiological mechanism include (Harrisons)
    • (1) diffuse microangiopathy, 
    Paradoxically, the process of revascularization that normally reestablishes blood flow to ischemic tissue is defective in SSc despite elevated levels of other angiogenic factors. Moreover, bone marrow–derived circulating endothelial progenitor cells are reduced in number and impaired in function. Widespread capillary loss, obliterative vasculopathy of small and medium-sized arteries, and impaired ability to repair and replace damaged vessels are hallmarks of SSc.
    • (2) inflammation and autoimmunity, and 
    • (3) visceral and vascular fibrosis in multiple organs


    Immunopathogenesis: https://doi.org/10.1080/1744666X.2019.1614915

    Microvascular endothelial cell injury and apoptosis is a key first step in the SSc that drives the immunopathogenesis. 
    • highlighted in purple are processes involved in pathogenesis of SSc; added information in black is to show the comparison of SSc pathogenesis to the rest of the clinical immunology)
      • Innate and Adaptive Immune mechanisms are involved in pathogenesis. 
        • Innate Immune System
          • Physical Mucosal Barrier
          • Proteins
          • Cells like Granulocytes, NK Cells, Macrophages, Dendritic Cells
            • Plasmacytoid dendritic cells infiltrate the skin of SSc patients and are chronically activated, leading to secretion of interferon-. (IFN-.alpha) and small chemokine PF4, also known as CXCL4) which are both hallmarks of the disease.
          • Phagocytic defects
          • Cell Signalling including IFN Gamma: TLR activation from IFN produced by plasmacytoid dendritic cells 
            • Type 1 IFN INTERFERON SIGNATURE is noted in SSc
          • Complement (Alternate and Lectin Pathways)
        • Adaptive Immune System
          • T-Cell
            • T-Cell Development
            • T-Cell Maturation
            • T-Cell Activation and antigen presentation or Functioning 
                • T cells are also involved in SSc
              • Th1:
              • Th2 : SSc has TH2 cell activation 
                • CD4+ Interestingly, among T cells (T cells), the type 2 T helper (TH2) cells – characterized by secretion of IL-4 and IL-13 – are more expressed in SSc than TH1 cells, which primarily secreteanti-fibrotic IFN.
              • Th17: Also, implicated in SSC. T reg cells have been noted to transform into Th17 cells
          • B-Cell
            • Impaired Development
            • Impaired Functioning 
              • T-cell mediated
              • T-cel independent 
                • In diffuse cutaneous SSc (dcSSc) anti-topoisomerase AAbs

                  (ATA), formerly known as anti-Scl70 AAbs, are more prevalent,

                  whereas anticentromere AAbs (ACA) are more frequent

                  in limited cutaneous SSc (lcSSc).

                  A possible pathogenic role of ATA in SSc has been suggested

                  following its binding to fibroblasts and induced adhesion and

                  activation of cocultured monocytes [48]. This observation might

                  provide an explanation for the amplification of the fibrogenic

                  cascade in ATA-positive SSc patients.


        • Regulatory Immune System
          • Innate System Regulation
            • Regulatory cell dysfunction is noted in SSc. Decreased regulatory T cells in circulation is noted. Also, these regulatory Tcells can transform into pathogenic effector T Cell 
          • Adaptive System Regulation







    American College of Rheumatology/European League against Rheumatism Classification Criteria for the Classification of Systemic SclerosisModified from van den Hoogen F, Khanna D, Fransen J, et al: 2013 classification criteria for systemic sclerosis: an American College of Rheumatology/European League against Rheumatism collaborative initiative. Arthritis Rheum 65:2737–2747, 2013.
    ItemSub-item(s)Weight/Score*
    Skin thickening of the fingers of both hands extending proximal to the metacarpophalangeal joints (sufficient criterion)9
    Skin thickening of the fingers (only count the higher score)Puffy fingers2
    Sclerodactyly of the fingers (distal to the MCPs but proximal to the proximal interphalangeal joints)4
    Fingertip lesions (only count the higher score)Digital tip ulcers2
    Fingertip pitting scars3
    Telangiectasia2
    Abnormal nailfold capillaries2
    Pulmonary arterial hypertension and/or interstitial lung disease (maximum score 2)Pulmonary arterial hypertension2
    Interstitial lung disease2
    Raynaud’s phenomenon3
    SSc-related autoantibodies (maximum score is 3)ACA
    Scl-70
    RNA Pol
    3

    ACA, Anticentromere; MCPs, metacarpophalangeal joints; RNA Pol, anti-RNA polymerase III; Scl-70, antitopoisomerase 1; SSc, systemic sclerosis.



    Ms. B
    70 yo F WITH NSIP, SCLERODACTALY, NO CAPILLARY EVIDENCE OF ABNORMAL BLOOD VESSELS. HX OF RAYNAUDS, PBC, AIH. 

    2 for diffuse: SCL70; RNA Pol III
    2 for both: U3RNP, B23, 
    3 for limited : Anticentromere, Th/TO, APLA
    3 for OverlaP: PM/SCL; U1RNP (MCTD- PM, SCL, SLE); ANti-KU (muslce and joint); 


    The speckled nuclear staining pattern (left) can be detected in 30% of patients with diffuse scleroderma and suggests the presence of anti–topoisomerase I antibodies.

    The homogeneous nucleolar staining pattern (center) is detected in 25 to 50% of patients with the myositis–scleroderma overlap syndrome

    A pattern characterized by the clumping of the nucleoli  is highly specific for diffuse scleroderma (in 5% of patients).

    Nucleolar antigens are RNA polymerases, fibrillarin, Th/To, or PM-Scl. 

    The anticentromere-antibody staining pattern (right) can be detected in 70 to 80% of patients with limited cutaneous scleroderma 

    The antigens for anticentromere-ab is kinetochore proteins of the centromere regions of chromosomes.


    Up to 11% of patients with scleroderma can test negative for anti-nuclear antibodies (ANAs).
    AntigenSubtypeClinical Phenotype
    Topoisomerase 1 (Scl-70) ABSENT as no evidence of diffuse diseaseDiffusePulmonary fibrosis, cardiac involvement
    Centromere (protein B, C)
    ABSENT as no evidence of digital ischemia or PAH or calcinosis
    LimitedSevere digital ischemia, PAH, sicca syndrome, calcinosis
    RNA polymerase III
    Not checked but no evidence of severe skin disease, renal crisis
    DiffuseSevere skin disease, tendon rubs, cancer, GAVE, renal crisis (±sine scleroderma)
    U3-RNP (fibrillarin) - predictor of internal organ involvementDiffuse or limitedPrimary PAH; esophageal, cardiac, and renal involvement; muscular disease
    Th/To
    Good chance this may come positive
    LimitedPulmonary fibrosis, rare renal crisis, lower GI dysfunction
    B23
    Good chance this may come positive
    Diffuse or limitedPAH, lung disease
    Cardiolipin, β2GPILimitedPAH, digital loss
    PM/SclOverlapMyositis, pulmonary fibrosis, acro-osteolysis
    U1-RNPOverlapSLE, inflammatory arthritis, pulmonary fibrosis


    How to measure sclerodactaly? 


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