A case of juvenile Sjögren's syndrome with interstitial nephritis.

Primary Sjögren's syndrome (SS) is a rare autoimmune disease, especially in children. Juvenile primary SS with interstitial nephritis is rare in Japan. We report on a 12-year-old girl in whom salivary gland swelling had recurred from the age of 5 years, SS was diagnosed at the age of 10 years, and interstitial nephritis developed at the age of 12 years. The patient presented with a chief complaint of swelling of both parotid glands. The patient had a history of recurrent parotitis from 5 years of age, with episodes recurring 5 to 6 times a year and resolving within 3 days each time. However, at the age of 11 years, the patient had continuous mild swelling of the parotid glands. Examination on admission showed bilateral nontender parotid gland swelling; mild swelling of the lower extremities, xerostomia, and xerophthalmia but no exanthem. Laboratory findings were as follows: serum protein, 10.1 g/dL; immunoglobulin (Ig) G, 3,828 mg/dL; antinuclear antibodies, 1,280-fold; anti-Ro/SS-A antibody, 512-fold; anti-Ro/SS-B antibody, 4-fold; creatinine, 0.45 mg/dL; blood β2-microglobulin, 2.2 mg/L (slightly elevated); and cystatin C, 0.86 mg/L. Urinalysis showed proteinuria and a β2-microglobulin concentration of 11,265 mg/L. Thus, this patient had low molecular weight proteinuria. Schirmer's test showed decreased tear secretion (5 mm), and fluorescein staining showed marked bilateral superficial punctate keratitis. A lip biopsy showed infiltration by small round cells (mild to moderate), interstitial fibrosis, loss of salivary gland parenchyma, and atrophy, with no obvious epimyoepithelial islands, leading to a diagnosis of SS. Light microscopic examination of the renal biopsy specimens showed expansion of mononuclear cell infiltration in the renal interstitium, inflammatory cell infiltration of interstitial areas with edema and mild fibrosis, and tubulitis and mononuclear cell infiltration that included many lymphocytes and plasma cells. There were no pathological findings of glomerulonephritis. Small arteries showed no obvious abnormalities. Immunofluorescent staining showed slight, nonspecific deposition of IgM, but no deposition of IgG, complement 1q, 3, or 4. On the basis of the renal biopsy showing nonspecific chronic interstitial nephritis, renal tubular atrophy, and interstitial enlargement, tubulointerstitial nephritis associated with SS was diagnosed.