Morphologic findings in progressive familial intrahepatic cholestasis 2 (PFIC2): correlation with genetic and immunohistochemical studies

Abstract

Progressive familial intrahepatic cholestasis, type 2 (PFIC2), characterized by cholestasis in infancy that may progress to cirrhosis, is caused by mutation in ABCB11, which encodes bile salt export pump (BSEP). We correlated histopathologic, immunohistochemical, and ultrastructural features in PFIC2 with specific mutations and clinical course. Twelve patients with clinical PFIC2 and ABCB11 mutations were identified, and 22 liver biopsy and explant specimens were assessed. All had hepatocellular cholestasis; most had canalicular bile plugs. At least 1 specimen from every patient had centrizonal/sinusoidal fibrosis, often with periportal fibrosis. Neonatal hepatitis-like features (inflammation, giant cells, necrosis) varied. In 2 of the 5 patients with paired specimens obtained >6 months apart, lobular and portal fibrosis worsened. Transmission electron microscopy (EM) in all 9 patients studied showed canalicular dilatation, microvilli loss, abnormal mitochondrial internal structure, and varying intracanalicular accumulation of finely granular bile. Canalicular staining for BSEP was absent in 10 patients and present in 2 patients, 1 of whom had intermittent symptoms. ABCB11 sequencing of all patients identified 6 novel and 10 previously described mutations, with nonsense, missense, and/or noncoding mutations in the 10 patients without immunohistochemically demonstrable BSEP. Missense and/or noncoding mutations were identified in the 2 patients with demonstrable BSEP, whose clinical course was more indolent. Mutations ending ABCB11 transcription appear linked, through hepatocellular necrosis and fibrosis, to worse outcome. In conclusion, light microscopy and electron microscopy findings in clinical PFIC2 can support diagnosis, but are variable and nonspecific. Therefore, no correlation between specific mutations and histopathology is yet possible.

FIGURE 1

Light microscopy findings in PFIC2 include varying lobular inflammation, portal inflammation, giant cell transformation, hepatocellular necrosis, hepatocellular swelling, portal fibrosis, and centrizonal/sinusoidal fibrosis. A and B, Explanted liver of patient 12 at the age of 17 months shows cholestasis, focal lobular inflammation, hepatocellular necrosis (including necrotic giant cells), prominent centrizonal fibrosis, and stage 2 portal fibrosis. Hematoxylin and eosin (H&E; × 400) and trichrome (× 100) stains. C and D, Explanted liver of patient 9 at the age of 7 years shows more prominent, diffuse lobular inflammation and areas of bridging fibrosis (shown) and nodule formation (not shown) with architectural distortion. H&E (× 400) and trichrome (× 100) stains. E and F, Explanted liver of patient 6 at the age of 16 months shows giant cells, hepatocyte swelling, and centrizonal/sinusoidal fibrosis, all prominent, and cirrhosis. Patchy intense lobular inflammation and pervasive bands of vascularized intralobular replacement fibrosis are seen. Central veins and portal-to-portal scars are not discernible; most of the fibrosis is pericellular. H&E (× 160) and trichrome (× 100) stains.

FIGURE 2

Patient 7 had early-onset, intermittent pruritus and a long course (present age, 15 y), and his liver tissue showed intact canalicular BSEP immunostaining. Multiple liver biopsy specimens (A to D) showed stable liver disease with exacerbations of lobular cholestasis and hepatitis. A and B, Minimal cholestasis, occasional multinucleate giant hepatocytes, absent portal tract inflammation, and centrilobular fibrosis confined to zone 3 at the age of 13 months. C indicates central vein. Hematoxylin and eosin (H&E) and trichrome stains (each × 100). C and D, Mild portal and focal lobular inflammation (arrow) accompany lobular cholestasis and mild cell swelling at the age of 9 years. Fibrosis is mild. H&E and trichrome stains (each × 100) C indicates central vein. E, Immunostain for BSEP (hematoxylin counterstain) performed on liver biopsy tissue of patient 7 at the age of 9 years shows normal intensity and distribution of canalicular reactivity (× 200). F, In contrast, liver biopsy of patient 10 at the age of 21 months shows no canalicular reactivity. Immunostain for BSEP, hematoxylin counterstain (× 200).

FIGURE 3

Ultrastructural abnormalities of liver tissue were similar in the 9 patients studied. A, Liver biopsy from patient 7 at the age of 13 months shows canalicular dilatation, subtotal effacement of microvilli, a pericanalicular collar of microfilaments, and intact desmosomes. Canalicular bile is finely granular. Inset: Another severely dilated canaliculus in this patient contains occasional coarse aggregates mixed with the finely granular bile. Osmium tetroxide/uranyl acetate/lead citrate stain (× 3150). B, Liver biopsy from patient 11 at the age of 3 years shows mild mitochondrial pleomorphism, with alterations in size, shape, and matrix density. Osmium tetroxide/uranyl acetate/lead citrate stain (× 2000).