Treat underlying illness, if known
Manage critical complications: see treatment section of diffuse alveolar hemorrhage, acute limb ischemia, Kawasaki
For primary<unk> es, this will likely involve an immunosuppressive agent, such as:
Prednisone/Methylprednisolone
Cyclophosphamide, methotrexate, azathioprine
Rituximab
May consider plasmapheresis for severe or rapidly progressive
Prednisone/Methylprednisolone
Cyclophosphamide, methotrexate, azathioprine
Rituximab
Vasculitis syndromes
Abnormal platelet count and/or coagulation
Rickets
Septicemia
Lymphangitis
Idiopathic thrombocytopenic purpura 
Deep venous thrombosis
Hemolytic uremic syndrome