Plasma-negative, Renal-limited Cryofibrinogen-associated Glomerulonephritis: A Unique Case Report.

Cryofibrinogen-associated glomerulonephritis is characterized by membranoproliferative glomerulonephritis without immunoglobulin deposition and unique ultrastructural features. This case report presents a 63-year-old man with renal-limited cryofibrinogen-associated glomerulonephritis, with negative plasma cryofibrinogen levels. His medical history included metallic aortic valve replacement and long-term anticoagulation therapy. Clinical examination revealed no cutaneous manifestations or thrombotic events. Initial laboratory investigations showed severe kidney dysfunction, but negative results for plasma cryofibrinogen, serum cryoglobulin, and a comprehensive autoimmune, infective, and malignancy panel. Kidney biopsy revealed mesangiocapillary glomerulonephritis with focal vasculitis and significant interstitial fibrosis, and electron microscopy identified double-walled microtubules consistent with cryofibrinogen. Our patient was managed without immunosuppressive therapy due to significant kidney scarring and absence of extra-renal manifestations. To our knowledge, this case describes the first report of cryofibrinogen-associated glomerulonephritis in the absence of detectable cryofibrinogen in serum, with diagnosis relying on ultrastructural findings. Differential diagnoses such as immunotactoid glomerulonephritis were considered but ruled out based on morphological characteristics. This case adds to the limited literature on renal-limited cryofibrinogen and emphasizes the necessity for thorough investigation including electron microscopy assessment of kidney biopsies to ascertain the diagnosis.