What are the key clinical features that suggest a diagnosis of Microscopic Polyangiitis (MPA) in a patient presenting with systemic symptoms?

Microscopic Polyangiitis (MPA) is a necrotizing small-vessel vasculitis that typically presents with systemic symptoms and often affects multiple organ systems Lhote et al. 1996Chevet et al. 2023. It is a form of ANCA-associated vasculitis (AAV) and is commonly associated with myeloperoxidase (MPO)-ANCA, also known as p-ANCA Chevet et al. 2023Sharma et al. 2024.

Key clinical features suggesting MPA include:

• Renal involvement: Rapidly progressive glomerulonephritis (RPGN) is a hallmark feature, often leading to renal failure Lhote et al. 1996Chevet et al. 2023.
• Pulmonary involvement: Pulmonary capillaritis, which can manifest as alveolar hemorrhage, is another common and serious presentation Lhote et al. 1996Chevet et al. 2023. Patients may present with hemoptysis or dyspnoea Lhote et al. 1996.
• General systemic symptoms: Non-specific symptoms such as fever, weight loss, malaise, and fatigue are frequently reported Lhote et al. 1996.
• Musculoskeletal symptoms: Myalgia and arthralgia are common Lhote et al. 1996.
• Skin manifestations: Palpable purpura is a characteristic skin lesion that may be present Lhote et al. 1996.
• Neurological involvement: Peripheral neuropathy can occur Lhote et al. 1996.
• Gastrointestinal involvement: Abdominal pain, bleeding, or other gastrointestinal symptoms may be present Lhote et al. 1996.

While the provided UK guidelines NICE CKS,NICE NG239 do not specifically address Microscopic Polyangiitis, the diagnosis relies heavily on the combination of these clinical features, serological testing for ANCA, and often biopsy confirmation Chevet et al. 2023Sharma et al. 2024.