A 39-year-old man with no toxic habits, allergic to acetylsalicylic acid (ASA) and diclofenac. He initially consulted for soft tissue swelling associated with palpable purpura in both lower limbs in April 2001. Immunological tests revealed positive cryoglobulinaemia with a cryocrit of 9.2% (IgM kappa monoclonal IgM and IgG component). Serologies for hepatotropic viruses and human immunodeficiency virus (HIV) were negative, as were antiphospholipid antibodies.
Physical examination revealed palpable purpura in the lower extremities; the rest of the examination was unremarkable. A thoracoabdominal computed tomography (CT) scan showed no lymphadenopathy or visceromegaly. With the suggestion of cutaneous vasculitis, treatment was started with prednisone at a dose of 1 mg/kg/day, with an initial favourable evolution and disappearance of the lesions.
One year after the first consultation, the patient reported paresthesia in the lower limbs, again associated with petechiae in the same location, this time presenting with nephritic syndrome. Laboratory tests showed hypocomplementemia, a cryocrit of 17% and a proteinogram with a faint abnormal band in the gamma zone. Serum immunoelectrophoresis: restricted mobility component IgM kappa (there was no evidence of monoclonality in the urine). Renal function showed creatinine 1.2 mg/dl, sediment with red blood cells +++ and proteinuria 2.8 g/day.
Renal biopsy confirmed the presence of glomerulonephritis with mesangiocapillary pattern. Azathioprine was added to the treatment, with maintenance of renal function and proteinuria of around 1g.

After six years of follow-up, an analytical control revealed a peripheral blood immunophenotype compatible with LLP. This finding was later corroborated with a bone marrow aspirate in which bone marrow infiltration by chronic small B-cell lymphoproliferative syndrome was observed, compatible with quiescent LLP, so at that time he did not require chemotherapy treatment.
One year later, the patient presented persistent proteinuria of 4.7 g/24 h, so it was decided to perform a new renal biopsy that confirmed the presence of cryoglobulinemic glomerulonephritis and also showed lymphocytic infiltration compatible with low-grade B lymphoma. Given the renal involvement by the lymphoma, it was decided to start treatment with rituximab at a dose of 375 mg/m2 subcutaneous (s.c.) x 4 and plasma exchange.

Two years after anti-CD20 treatment, the patient has lymphoproliferative syndrome in remission and renal involvement is maintained in the form of residual proteinuria (4 g/day) with preserved renal function (Cr 0.8 mg/dl, GFR: 100 ml/min) under treatment with double blockade of the renin-angiotensin-aldosterone axis.