You are here

Microscopic polyangiitis G042

Last amended 
14 October 2019
Current RMA Instruments
Reasonable Hypothesis90 of 2019
Balance of Probabilities91 of 2019
Changes from previous Instruments

SOP bulletin 211

ICD Coding
  • ICD-9-CM Codes: 446.29
  • ICD-10-AM Codes: M31.7
Brief description

This is a type of small vessel vasculitis (inflammation of blood vessels). The acute inflammation leads to the death (necrosis) of part of the vessel and is associated with thrombosis. This then leads to scarring of the blood vessel which can lead to obstruction. This type of vasculitis only affects arterioles, capillaries and venules.

The clinical manifestations depend upon the organs involved and relate to ischaemia and infarction brought on by the vascular lesions. The organs involved most commonly are the kidney (glomerulonephritis) and the lungs. Other sites of involvement include: skin; ear, nose and throat; eyes; and nervous system.

Confirming the diagnosis 

This diagnosis is complex and difficult.  Specialist physician opinion is required.  Typically, a histologic biopsy of blood vessels at a site of active disease will be performed. Distinguishing features include the absence of granuloma formation and the presence of a necrotizing vasculitis.  There are other types of vasculitis that have very similar clinical presentations and serological findings, that need to be distinguished.

The relevant medical specialist is a physician (nephrologist if kidney involvement, respiratory physician if lung involvement).

Additional diagnoses covered by SOP

  • Nil
Conditions excluded from SOP
  • Churg-Strauss syndrome#
  • Disseminated necrotising periarteritis#
  • Drug related vasculitis#
  • Eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)#
  • Giant cell or temporal arteritis*
  • Granulomatosis with polyangiitis (Wegener granulomatosis)#
  • Hypersensitivity vasculitis#
  • Necrotising angiitis#

  • Panarteritis or periarteritis (nodosa)#

  • Polyangiitis overlap syndrome#
  • Polyarteritis with lung involvement#
  • Polyartertitis nodosa*
  • Thromboangiitis obliterans (Buerger’s disease)*
  • Wegener’s granulomatosis#

* Another SOP applies

# non-SOP condition 


Clinical onset

This condition can present slowly over months or explosively over days. Initial manifestations are typically non-specific, e.g.  fever, malaise, anorexia, and weight loss.  More organ specific symptoms may also be present initially, particularly ENT, lung and skin symptoms.

Clinical worsening

The clinical course is variable.  The condition is often responsive to immunosuppresive treatment and remission can be achieved in most patients.  The condition can have a relapsing-remitting course. Treatment resistance may develop and in some people severe end-stage renal disease or other organ damage can develop, with the condition becoming fatal.