title: Enthesitis as a component of dactylitis in psoriatic juvenile idiopathic arthritis: histology of an established clinical entity.
abstract: BACKGROUND
  Imaging of dactylitis in adult psoriatic arthritis suggests a pathophysiological role for enthesitis. However, histological definition of the dactylitic digit is unavailable.
  
  
  OBJECTIVE
  We evaluated the role of enthesitis in dactylitis associated with psoriatic juvenile idiopathic arthritis (psJIA) in a child who underwent detailed imaging and histologic evaluation.
  
  
  METHODS
  Radiographs, ultrasound and high-resolution magnetic resonance imaging were employed to define the locus of disease in two dactylitic digits from a 14-year-old girl with psJIA. Biopsies were stained with hematoxylin and eosin, CD3, CD20, CD4, CD8 and CD117 and examined via light microscopy.
  
  
  RESULTS
  Radiologic features of dactylitis included enhanced signal at digital entheses without accompanying synovitis or tenosynovitis. Histologically, finger and toe tissue exhibited hypervascular tenosynovium with a fibromyxoid expansion of fibrous tissue. This was accompanied by sparse to moderate perivascular lymphocytic inflammation consisting predominantly of T cells, with occasional admixed B cells and mast cells. Neutrophils and plasma cells were absent. Fibrocartilage exhibited reactive features including increased extracellular myxoid matrix, binucleation, and focal necrosis, without cellular inflammation. Fibrinous synovitis and mild reactive synoviocyte hyperplasia were seen.
  
  
  CONCLUSIONS
  Dactylitis in psJIA bears a radiographic resemblance to the condition in adult psoriatic arthritis. Histologic hallmarks include an expanded mast cell-populated extracellular myxoid matrix, cartilage degeneration, and a T cell-rich perivascular inflammatory infiltrate. These findings help to define enthesitis as a clinicopathologic entity.
authors.affiliation: Division of Immunology, Boston Children's Hospital, Boston, MA USA.
authors.forename: Katherine S L
authors.initials: KS
authors.lastname: Tuttle
authors.affiliation: Department of Pathology, Boston Children's Hospital, Boston, MA USA.
authors.forename: Sara O
authors.initials: SO
authors.lastname: Vargas
authors.affiliation: Department of Radiology, Boston Children's Hospital, Boston, MA USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Callahan
authors.affiliation: Department of Orthopedic Surgery, Boston Children's Hospital, Boston, MA USA.
authors.forename: Donald S
authors.initials: DS
authors.lastname: Bae
authors.affiliation: Division of Immunology, Boston Children's Hospital, Boston, MA USA ; Division of Rheumatology, Immunology, and Allergy, Brigham and Women's Hospital, Smith 516B, One Jimmy Fund Way, Boston, MA 02115 USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Nigrovic
mesh_terms: D000293:Adolescent; D018501:Antirheumatic Agents / Q000627:therapeutic use; D001171:Arthritis, Juvenile / Q000188:drug therapy / Q000473:pathology* / Q000503:physiopathology*; D002357:Cartilage Diseases / Q000473:pathology; D000068800:Etanercept; D005109:Extracellular Matrix / Q000473:pathology; D005260:Female; D005384:Finger Joint / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D007074:Immunoglobulin G / Q000627:therapeutic use; D008727:Methotrexate / Q000627:therapeutic use; D018124:Receptors, Tumor Necrosis Factor / Q000627:therapeutic use; D012216:Rheumatic Diseases / Q000188:drug therapy / Q000473:pathology* / Q000503:physiopathology*; D013601:T-Lymphocytes / Q000473:pathology; D014033:Toe Joint / Q000473:pathology / Q000503:physiopathology; D016896:Treatment Outcome
chemical_list: D018501:Antirheumatic Agents; D007074:Immunoglobulin G; D018124:Receptors, Tumor Necrosis Factor; D000068800:Etanercept; D008727:Methotrexate
keywords: Dactylitis; Enthesitis; Enthesitis related arthritis; Juvenile idiopathic arthritis; Psoriatic arthritis; Psoriatic juvenile idiopathic arthritis