We read with great interest the article by Lewindon et al.1 The authors elegantly addressed the issue of hepatic disease in the natural history of patients with cystic fibrosis (cystic fibrosis–associated liver disease [CFLD]). Liver fibrosis, ranging from grade 1 to 4, was detected by dual-pass biopsy in most of the patients (77.5%). Incident portal hypertension (PHT) occurred in up to 42% of patients. Notably, clinical characterization did not predict the individual's risk of liver fibrosis or PHT, whereas dual-pass liver biopsy was informative of such risk.
The need for noninvasive, user-friendly, and quick techniques to quantify liver fibrosis in systemic disease also emerges for cystic fibrosis. Novel tissue strain imaging techniques, i.e., transient elastography2 or acoustic radiation force impulse imaging (ARFI),3 may represent valuable options in the evaluation and follow-up of CFLD. ARFI is an imaging technique that involves targeting an anatomic region to be interrogated for elastic properties with use of a region-of-interest cursor while performing real-time B-mode imaging.3
Here, we report results of ARFI evaluation (ACUSON S2000; Siemens, Erlanger, Germany) in 40 patients affected by cystic fibrosis (age 12 ± 5.1 years). Ten successful measurements of shear-wave speed were obtained in each patient in the deep right lobe, taking care not to capture any vascular or biliary structure. Diagnosis of PHT was based on presence of splenomegaly and esophageal varices. Patients with PHT (n = 12, Fig. 1A,B) had significantly greater median velocities (1.56 ± 0.47 versus 1.1 ± 0.19 m/second; P = 0.001) and velocities at each measurement (P from 0.046 to 0.001) than patients who were free of PHT (n = 28, Fig. 1C,D). The receiving operating characteristic (ROC) analysis was applied to evaluate ability of speed measurement to detect PHT (area under the ROC curve = 0.82, 95% confidence interval 0.65-0.98; P = 0.002). On ROC analysis, the cutoff value of 1.3 m/second, previously reported as diagnostic in adults with fibrosis from viral hepatitis,3 had sensitivity of 0.75 and specificity of 0.79. Thus, ARFI seems to be an accurate methodology to investigate CFLD. Nevertheless, accuracy to assess grade of fibrosis, reproducibility, and diagnostic cutoff values for shear-wave speed should be carefully evaluated in larger and controlled studies.
We congratulate the authors on the emphasis they put on the importance of liver fibrosis staging in patients with cystic fibrosis,1 and we certainly agree that liver biopsy must be considered in management of such patients unless noninvasive techniques are validated.