= Synovitis, Acne, Palmoplantar pustulosis, Hyperostosis, Osteitis

= PUSTULOTIC ARTHROSTEITIS = STERNOCLAVICULAR HYPEROSTOSIS

= association of sterile osteoarticular inflammation with skin abnormalities (palmoplantar pustulosis + severe acne)

◊Delay of several years can separate osseous from cutaneous lesions! Many patients have endured years of consultations and unnecessary invasive procedures before receiving the correct diagnosis!

Etiology: ? variant of psoriasis, exaggerated immune response in genetically susceptible individuals to Propionibacterium acnes

Age: young to middle-aged adults; M÷F = 1÷1

Histo: osteolytic portion of bone lesion contains plasma cells

• palmoplantar pustulosis (52%) = chronic eruption of yellowish intradermal sterile 2–4 mm monomorphic pustules limited to palms + soles
• acute severe acne (15%) = acne fulminans, acne conglobata, hidradenitis suppurativa → sudden eruption of highly inflammatory tender ulcerative nodules + plaques with hemorrhagic crust on face, back, chest
  Organism: Propionibacterium acnes (= anaerobe typically found in acne lesions)
  • blood + bone cultures usually negative
• chronic relapsing-remitting course with pain, soft-tissue swelling, limitation of motion at skeletal site of involvement (most often in anterior chest wall) ± fever
  ± elevated erythrocyte sedimentation rate + C-reactive protein
• rheumatoid factor negative + human leukocyte antigen (HLA)–B27 positive = seronegative spondyloarthropathy
• bone sclerosis combined with variable degree of osteolysis and periostitis:
  • medullary trabecular changes = osteitis
  • cortical hyperostosis in long-standing disease
• accompanied by adjacent inflammatory arthritis ± enthesitis + ankylosis

Bone scintigraphy:

• often reveals asymptomatic skeletal lesions
• Sternoclavicular joint (70–90%)
  Age: adulthood + childhood
  Site: manubrium sterni, insertion of costoclavicular ligament, clavicles with mediolateral progression
  • osteolysis at beginning of disease
  • hyperostosis + osteosclerosis later in disease
  • ankylosis of sternoclavicular joint
  • DIAGNOSTIC costoclavicular enthesopathy + small hyperostotic foci at sternal end of 1^st ribs
  
  NUC (bone scintigraphy):
  • “bull's head” sign = increased radiotracer uptake in manubrium + both sternoclavicular joints (HIGHLY SPECIFIC)
• Axial skeleton (33%)
  Age: adulthood
  • homogeneous osteosclerosis / osteolysis of one / more vertebral bodies (usually monovertebral) → collapse
  • disk space narrowing + endplate erosion (mimicking infectious spondylodiskitis)
  • sclerosis + expansion (mimicking Paget disease)
  • asymmetric bulky paravertebral ossification + sacroiliitis (mimicking psoriatic arthritis):
    • paravertebral ossifications (mimicking marginal / nonmarginal syndesmophytes / massive bridging)
    • unilateral sacroiliitis + associated osteosclerosis of adjacent iliac bone
  
  MR:
  • focal / diffuse marrow signal abnormality with enhancement (= edema / osteitis)
  • hyperintense paravertebral soft-tissue swelling
  • endplate irregularities + CHARACTERISTIC anterior vertebral body corner erosion at multiple levels
  • increased disk signal intensity on T2WI
  • disk enhancement after contrast administration
  
  DDx: infectious spondylitis (abscess, epidural involvement, single level of involvement)
• Appendicular skeleton (30%)
  Age: childhood
  • chronic recurrent multifocal osteomyelitis (misnomer)
  
  Location: distal femur, proximal tibia, fibula, humerus, radius, ulna, rib
  Site: metaphysis
  • osteosclerosis / osteolysis + periosteal new bone formation + bone expansion with aggressive appearance
• Joints
  Location: knee, hip, ankle, DIP of hand
  • synovial inflammation with juxtaarticular osteoporosis (early)
  • joint narrowing, marginal erosion, hyperostosis, enthesopathy (later)

Prognosis: chronic course with unpredictable exacerbations + remissions

Dx: sterile culture of osseous lesion

Rx: nonsteroidal antiinflammatory drugs, corticosteroids, methotrexate, tumor necrosis factor α inhibitor, analgesics, cyclosporine

DDx: infectious osteomyelitis / spondylitis, chronic recurrent multifocal osteomyelitis, osteosarcoma, Ewing sarcoma, metastasis, Paget disease, aseptic necrosis of clavicle