Distinguishing C1q nephropathy from lupus nephritis

'Seronegative lupus nephritis' describes patients with renal histology typical of lupus nephritis who have no clinical or serological evidence of systemic lupus erythematosus (SLE). We report our experience in nine patients identified as having 'seronegative lupus nephritis' who met the diagnostic criteria for C1q nephropathy.

A retrospective review of clinical case notes and renal histology was carried out.

We describe nine patients with C1q nephropathy in whom the diagnosis of 'seronegative lupus nephritis' was initially considered. All had renal histological features typical of lupus nephritis with 'wire loop' appearances on light microscopy, 'full house' immunoglobulin and complement deposition by immunoperoxidase, and electron-dense deposits in at least two glomerular locations. None of these nine patients developed clinical or serological evidence of SLE over a median follow-up of 6 years (range 0.1-9). There was no consistent evidence of a response to immunosuppressive therapy. In all cases, C1q staining was dominant on immunoperoxidase, and no tubuloreticular inclusions were seen. These appearances accord with previous descriptions of C1q nephropathy.

The implications of a diagnosis of lupus are considerable, and we propose that the term 'seronegative lupus nephritis' is unhelpful, and should be avoided when there is diagnostic uncertainty. The term C1q nephropathy should be preferred when these histological features are seen in the absence of overt lupus, when C1q deposition is dominant and when tubuloreticular bodies are absent. The clinical course in the cases reported here does not support the use of immunosuppressive therapy in C1q nephropathy.