18th February 2025

Microscopic polyangiitis

Microscopic polyangiitis (MPA) is an ANCA-associated necrotising vasculitis without granulomatous inflammation. It predominantly affects small vessels including the lungs and kidneys. Features and presentation are similar to GPA, but it typically lacks upper respiratory tract involvement. 

MPA is generally associated with p-ANCA (versus c-ANCA in GPA) but either can be positive. MPA may still be the preferred diagnosis even with a positive c-ANCA over GPA if there are no ear, nose or throat nor upper respiratory features, although they can be difficult to distinguish.

The most common pulmonary manifestation is pulmonary haemorrhage, which can be seen in up to 40% of cases. Other clinical features, as well as investigation and management, are similar to GPA. Some classify the term of idiopathic pauci-immune pulmonary capillaritis (IPIPC) as a lung-specific subtype of MPA as it is also associated with p-ANCA.

Treatment is with IV methylprednisolone and cyclophosphamide/rituximab.