Renal involvement in systemic amyloidosis--an Italian retrospective study on epidemiological and clinical data at diagnosis.

BACKGROUND: Few data are available on epidemiology and clinical picture of renal involvement in different forms of systemic amyloidosis.
METHODS: Patients with biopsy-proven systemic amyloidosis diagnosed in Italy between January 1995 and December 2000 were selected from 49 Nephrology and Internal Medicine Units provided they showed signs characteristic of renal involvement. Clinical and laboratory information were collected by using a specific data form for diagnosis integrated by a questionnaire on diagnostic tools. Collected data were matched both with the Italian Registry of Renal Biopsies (IRRB) and the Registry of the Italian Society of Amyloidosis (SIA) in order to approximate the incidence of the disease.
RESULTS: Of all patients, 373 were finally selected throughout Italy with an estimated mean incidence of renal amyloidosis of 2.1 per million population (p.m.p.) per year. Of those, 237 were affected from AL (primary) amyloidosis, 104 from AA (secondary) amyloidosis and 6 from AF (heredofamilial) forms. In 26 cases the type of amyloidosis remained undetermined. Among patients with AL, 36 presented an associated multiple myeloma (MM). Rheumatoid arthritis (RA) was the commonest underlying disease in AA. Median age ranged between 63 and 65 years in all groups. Males were prevalent in AL and females in AA. The main clinical features of renal involvement were represented by nephrotic syndrome and renal failure observed in 59 and 54% of cases, respectively. The presence of a lambda light chain, either in serum or urine was significantly associated to a more elevated urinary protein loss and to a reduced renal function. Patients with AA showed a worse renal function at presentation than patients with AL, possibly due to a late diagnosis and/or referral to nephrology units. Diagnosis was obtained by renal biopsy in 315 cases, by abdominal fat tissue (AFT) aspiration/biopsy in 156 patients and by other organ biopsies in 47 patients. Characterization of deposits was extremely variable among referring centres.
CONCLUSIONS: Our results point to an increased incidence of renal amyloidosis observed in Italy over the period 1996-2000 with AL as the prevalent type. Characterization of amyloid deposits still remains the major diagnostic challenge of the disease. The institution of networks dedicated to rare diseases is strongly recommended in order to effectively afford this challenge.