Morphological features of hepatic lipid changes in bearded dragons (Pogona vitticeps), and a proposed grading system

Abstract

Hepatic lipidosis is commonly diagnosed in pet bearded dragons ( Pogona vitticeps). However, there are no studies detailing the histological features of hepatic lipid changes in this species. This study describes the microscopic features of lipid change and details an associated scoring system. Histologic hepatic sections were retrospectively evaluated from 252 bearded dragons submitted for necropsy. Pathologic assessment was used to develop a grading scheme with 2 qualitative, 1 quantitative, and 6 semi-quantitative microscopic parameters, which were refined based on variability. The final grading system developed for diffuse and panlobular lipid accumulation included 2 semi-quantitative and 1 quantitative categories: percentage of hepatocellular vacuolation, fibrosis, and hepatocellular swelling, respectively. Hepatocellular swelling was indirectly quantified by counting the number of nuclei per unit area. There was a strong positive correlation ( P < .001) between the percentage of hepatocellular vacuolation and lipid content, a strong negative correlation ( P < .001) between nuclear count and lipid content, and a moderate correlation ( P < .001) between fibrosis and lipid content. Each category was given a numerical value ranging from 0 to 4, with the sum of each representing the final grade. Cutoff values stratified microscopic changes into mild (final grade 1–4), moderate (5–7), and severe (≥8). There was strong interrater agreement for assessment of vacuolization, fibrosis, and severity classification and moderate for hepatocellular swelling. This study documents the features of hepatic lipid changes in bearded dragons. Although a cutoff to differentiate pathologic from nonpathologic lipid accumulation could not be estimated, the proposed grading scheme can be used to inform future studies.

Association of plasma metabolites and diagnostic imaging findings with hepatic lipidosis in bearded dragons (Pogona vitticeps) and effects of gemfibrozil therapy

“…Additional stains including Periodic acid-Schiff, Masson's trichome, and Congo Red were utilized to further evaluate cases as needed. The grade and classification of hepatic lipid changes were determined for each histological sample according to a scoring system which assessed percent of hepatocellular vacuolation, fibrosis, and hepatocellular swelling by a blinded pathologist (LS) and an exotic animal veterinarian (TB), as previously described S1 Table [30]. In addition, the percentage of hepatic lipid was calculated using digital image analysis with an image processing program (ImageJ 1.53a) for each animal [66].…”

“…In addition, the percentage of hepatic lipid was calculated using digital image analysis with an image processing program (ImageJ 1.53a) for each animal [66]. Due to the physiological process of lipogenesis in the bearded dragon liver [10], and the histological evaluation of 252 cases [30], authors suspected that all vacuolated hepatocytes without cellular swelling were a variation of normal. Therefore, based on the grading system where cellular swelling placed cases in the moderate or severe class [30], cases with moderate to severe hepatic lipid changes were considered most likely to be diagnosed with hepatic lipidosis.…”

“…In the absence of reliable blood biomarkers, the diagnosis of hepatic lipidosis heavily relies on advanced imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI), or liver biopsies with histology [3,8,13,29]. To date, histology is the only validated diagnostic tool for hepatic lipidosis [3,29], and our group has recently proposed a grading system to assess the accumulation of fat and its effects on the hepatic tissue of bearded dragons [30]. However, due to the invasive nature, morbidity and mortality associated with sampling, and cost, histology is typically performed at a later stage in the disease in both human and veterinary medicine and so various imaging modalities continue to be investigated for earlier, non-invasive diagnosis [3,[31][32][33][34].…”

Prevalence and risk factors of hepatic lipid changes in bearded dragons (Pogona vitticeps)

“…1 Three hundred and seventy-four cases were not diagnosed with hepatic lipidosis in their original reports: 319 of these were scored 0 for final grade and severity tier, while 55 cases were reevaluated and graded. 1…”

“…One hundred and ninety-seven cases were diagnosed with hepatic lipidosis in the original report and were reevaluated histologically according to the grading scheme. 1 Three hundred and seventy-four cases were not diagnosed with hepatic lipidosis in their original reports: 319 of these were scored 0 for final grade and severity tier, while 55 cases were reevaluated and graded. 1…”