From fibrosis to diagnosis: a paediatric case of microscopic polyangiitis and review of the literature.

We herein describe a case of a 6-year-old girl diagnosed with microscopic polyangiitis (MPA) after a long diagnostic process demanding the cooperation of paediatric respiratory medicine specialists, rheumatologists, nephrologists and radiologist. First symptoms of MPA were observed after Mycoplasma pneumoniae infection and included persistent crepitations at the basis of both lungs and mild haematuria. CT imaging showed features of lung fibrosis, renal biopsy was indicative of mesangial proliferative glomerulonephritis, in the skin biopsy features of microscopic polyangiitis were described. In the laboratory tests pANCA antibodies specific for myeloperoxidase (MPO) were present in high titer. MPA with initial features of lung fibrosis is an unusual presentation of this rare disease, usually observed in adult population. This unique case illustrates the diagnostic and therapeutic challenges in paediatric vasculitis patients with an unusual initial presentation in the form of interstitial lung disease. In the manuscript we also discuss the possible aetiology of lung fibrosis in microscopic polyangiitis MPA and provide the review of the current literature on the topic of childhood-onset MPA.