Heavy chain deposition disease presenting with raised anti-GBM antibody levels; a case report.

<bold>Background: </bold>Monoclonal immunoglobulin deposition disease (MIDD) is a rare condition accounting for < 1% of histopathological diagnoses made on kidney biopsy1. The best outcomes are seen in those diagnosed and treated promptly, but delay to diagnosis is common with the largest series reporting a median time from onset of renal impairment to diagnosis of 12 months2. Here, we report a case of the heavy chain subset of MIDD presenting with positive anti-glomerular basement membrane (anti-GBM) antibodies obscuring the true diagnosis.<bold>Case Presentation: </bold>Here, we present a challenging case presenting with oedema, haematoproteiuria, and new renal impairment. Anti-GBM antibodies were positive and prompted treatment as atypical anti-GBM disease. However, they were ultimately proven to be monoclonal and secondary to myeloma. The final diagnosis facilitated effective myeloma treatment which led to complete remission and independence from renal replacement therapy.<bold>Conclusions: </bold>This case reinforces the importance of comprehensive histopathological and haematological assessment in making the correct diagnosis. Here it facilitated effective treatment and recovery of renal function. [ABSTRACT FROM AUTHOR]