Hyaline droplets in Kupffer cells: a novel diagnostic clue for autoimmune hepatitis.

Pediatric autoimmune hepatitis (AIH) is relatively common and has a characteristic but relatively nonspecific histopathology with a usually prominent lymphoplasmacytic infiltrate. Herein, we describe for the first time the presence of characteristic hyaline droplets in the cytoplasm of Kupffer cells on routine hematoxylin and eosin (H&E) sections in AIH. The medical records and pathologic material over a 20-year period (1992 to 2012) were reviewed from children with AIH (n=30), hepatitis B virus (n=30), and hepatitis C virus (n=30) from the pathology files at Boston Children's Hospital. All children had percutaneous needle liver biopsies. We reviewed sections stained with H&E, PAS, and PAS with diastase for the presence of hyaline droplets in all 90 biopsies. We also performed immunohistochemical analysis for IgG, IgA, and IgD in 6 biopsies with AIH. Hyaline droplets were identified in Kupffer cells throughout the lobules in 15 of 30 biopsies (easily found in 13 and rare in 2); conversely, no droplets were identified in 15. Droplets were identified in 10 AIH type 1 biopsies, 1 in AIH type 2, 3 in overlap syndrome, and 1 in unclassified. Serum IgG levels, when available, were correlated with biopsy findings. Seventeen patients had serum IgG levels available for review. The average IgG level in patients without droplets in their biopsies was 1364 mg/dL, in contrast to 3424 mg/dL in patients with droplets (P=0.021). Immunohistochemical analysis performed in 6 biopsies revealed that droplets were nearly always positive for IgG, occasionally for IgA, and rarely for IgD. None of the biopsies in patients with hepatitis C contained hyaline droplets. One biopsy of a patient with hepatitis B revealed hyaline droplets; this biopsy had an unusually prominent plasmacytic infiltrate, and the patient was found to have an elevated IgG serum level and antibodies to smooth muscle actin. As far as we are aware, hyaline droplets in Kupffer cells on routine H&E sections have never been described. They should be distinguished from the nonspecific granular lysosomal structures frequently found in Kupffer cells in a variety of chronic liver diseases and from erythrophagocytosis. Hyaline droplets may occur in AIH regardless of the type and correlate with a >2-fold increase in serum level of IgG as compared with patients without droplets in their biopsies. Identification of hyaline droplets in Kupffer cells provides a useful diagnostic clue to distinguish AIH from other forms of chronic hepatitis.