Cardiomyopathy in the Shadow of Fibrillary Glomerulonephritis: An Unusual Indirect Association.

Fibrillary glomerulonephritis (FGN) is a rare and complex renal disease where the accumulation of non-amyloid microfibrils composed of polyclonal immunoglobulin G within the mesangium and glomerular capillaries results in structural and functional abnormalities in the kidney's filtering units. The direct link between FGN and cardiomyopathy is not well established. However, it may be caused secondarily by systemic inflammation, uremia, or other overlapping factors and comorbidities. In our case, it was believed to be significantly influenced and worsened by various comorbid conditions, with hypertension being the most common cardiovascular risk factor in FGN itself, contributing to structural and functional cardiac impairment, including left ventricular hypertrophy and systolic dysfunction, rather than direct myocardial infiltration or damage by fibrillary deposit. We have a case of a 60-year-old female who presented with a severe manifestation of FGN, associated with secondary cardiomyopathy and renal failure complications, including hypertension-related issues, nephrotic syndrome with significant proteinuria, peripheral edema, anasarca, and shortness of breath, initially leading to hospitalization. Her renal insufficiency subsequently progressed to end-stage renal disease, and the discovery of a nephrotic range of proteinuria led to a kidney biopsy, confirming the diagnosis of FGN. Her renal recovery remained poor due to persistent volume overload, which impeded renal recovery and which required the initiation of dialysis. The patient experienced a rare cardiac involvement related to underlying FGN, which could not be confirmed through a cardiac biopsy because she chose to refuse this invasive test.  The treatment with prednisone and rituximab targeted FGN, reducing proteinuria and improving renal function, which allowed for a decrease in hemodialysis and normalization of the erythrocyte sedimentation rate and C-reactive protein at 12 months. Cardiac function also improved after six months, with lower brain natriuretic peptide levels, increased left ventricular ejection fraction (LVEF), and reversal of ventricular remodeling on echocardiogram, suggesting that early immunologic intervention can reverse cardiomyopathy and prevent progression. Longer follow-up is recommended, as improved LVEF is associated with a better prognosis in heart failure. FGN typically affects the kidneys, making cardiac issues uncommon. Therefore, further research is needed to understand the prevalence and mechanisms of cardiac involvement in FGN for developing targeted therapies.