Intermediate molecular weight proteinuria and albuminuria identify scleroderma patients with increased morbidity

Renal involvement and systemic vascular damage have been shown to significantly affect prognosis in systemic sclerosis (SSc). However, it is often difficult to assess damage to the renal and systemic vasculature in SSc patients.

Using detailed urinary protein analysis we sought to detect scleroderma renal disease at an early stage and to assess systemic vasculopathy due to SSc. We examined 80 patients with SSc as well as 18 healthy control subjects using urinary protein analysis including determination of urinary albumin excretion rate and urinary total protein excretion as well as urinary polyacrylamide gel electrophoresis.

Albuminuria was found in 25% (20/80) of the SSc patients (2.5% macroalbuminuria, 22.5% microalbuminuria), increased total protein excretion in 17.5% (14/80), and intermediate molecular weight proteinuria (IMWP) as determined by urine electrophoresis in 31.3% (25/80). None of these abnormalities was found in the control group (0/18). Presence of IMWP correlated with the diffuse type of SSc (p < 0.01), gastrointestinal involvement (p < 0.05) and increased systolic blood pressure (p < 0.01). Increased total protein excretion was found to correlate with pulmonary involvement (p < 0.05). Albuminuria was associated with prolonged duration of the disease (> 4 years) (p < 0.05) and increased systolic blood pressure (p < 0.01).

Leakage of proteins into the urine in patients with SSc appears to indicate not only renal involvement but also systemic vasculopathy which is associated with increased morbidity. Patients with SSc should be regularly examined using sensitive urinary protein tests such as albumin assays or urine electrophoresis, to detect kidney involvement at an early stage.