IgA nephropathy and IgA vasculitis nephritis: Viva

Branch 1: Diagnosis and the defining features

The candidate should recognise that this boy has IgA nephropathy and state the defining feature: dominant mesangial IgA deposition on immunofluorescence. The clinical clue is the synpharyngitic timing of the macroscopic haematuria, appearing within one to two days of the sore throat, which is the single most discriminating bedside feature. A strong candidate should emphasise that the normal C3 and C4 exclude post-infectious glomerulonephritis, which has a one to two week latency and a low C3, and exclude lupus and membranoproliferative disease for the same reason. ^[1]

If the examiner presses on pathogenesis, the candidate should explain the multi-hit hypothesis: production of galactose-deficient IgA1, formation of antiglycan autoantibodies against it, generation of circulating immune complexes, and mesangial deposition with complement activation. The candidate should note that this is the same mechanism shared by IgA vasculitis nephritis, which is why the renal lesions are histologically identical. ^[1]