PAS-positive lymphocyte vacuoles can be used as diagnostic screening test for Pompe disease

Abstract

Screening of blood films for the presence of periodic acid-Schiff (PAS)-positive lymphocyte vacuoles is sometimes used to support the diagnosis of Pompe disease, but the actual diagnostic value is still unknown. We collected peripheral blood films from 65 untreated Pompe patients and 51 controls. Lymphocyte vacuolization was quantified using three methods: percentage vacuolated lymphocytes, percentage PAS-positive lymphocytes, and a PAS score depending on staining intensity. Diagnostic accuracy of the tests was assessed using receiver operating characteristic (ROC) curves. All three methods fully discerned classic infantile patients from controls. The mean values of patients with milder forms of Pompe disease were significantly higher than those of controls, but full separation was not obtained. The area under the ROC curve was 0.98 for the percentage vacuolated lymphocytes (optimal cutoff value 3; sensitivity 91%, specificity 96%) and 0.99 for the percentage PAS-positive lymphocytes and PAS score (optimal cutoff value 9; sensitivity 100%, specificity 98%). Our data indicate that PAS-stained blood films can be used as a reliable screening tool to support a diagnosis of Pompe disease. The percentage of PAS-positive lymphocytes is convenient for use in clinical practice but should always be interpreted in combination with other clinical and laboratory parameters.

Fig. 1

Photomicrographs of blood films from patients with Pompe disease and a healthy control. a May-Grünwald/Giemsa-stained blood film of a late-onset Pompe patient showing a lymphocyte with two distinct vacuoles; b periodic acid-Schiff (PAS)-stained blood film of a healthy control (PAS score = 0); c PAS-stained blood film of a late-onset Pompe patient showing a lymphocyte with PAS-positive inclusions (PAS score = 2); d PAS-stained blood film of a patient with classic infantile Pompe disease showing a lymphocyte with a larger number of PAS-positive inclusions (PAS score = 3)

Fig. 2

Dot plots of a percentage of vacuolated lymphocytes, b percentage periodic acid-Schiff (PAS)-positive lymphocytes, and c PAS scores of 65 patients with Pompe disease and 51 controls. 0 controls (n = 51); 1 classic infantile patients (n = 8); 2 children with Pompe disease (n = 16); 3 adults with Pompe disease (n = 41)

Fig. 3

Receiver operating characteristic (ROC) curves for the percentage of vacuolated lymphocytes, percentage of periodic acid-Schiff (PAS)-positive lymphocytes, and PAS-score of 65 patients with Pompe disease and 51 controls. ——— percentage of vacuolated lymphocytes; •— —•— —• percentage of PAS positive lymphocytes; —— —— PAS score; •—•—• reference line