Increasing the number of minor salivary glands from patients with Sjögren's disease improves the diagnostic and measurement precision of the histological focus score

Minor salivary gland (MSG) biopsy has an important role in Sjögren's disease diagnosis and research. MSGs show within-patient variation in number of lymphocytic foci per unit area, but the optimal number of MSGs required to balance reproducibility and clinical acceptability has not been determined. Monte Carlo simulations were performed to investigate impact of MSG number on (i) diagnosis based on focus score (FS) ≥1; (ii) reproducibility, defined as the extent to which 2 FS measurements obtained from 2 within-patient biopsies are the same, assuming no systematic differences have occurred in between biopsies; and (iii) smallest sample size required to detect a clinically meaningful difference in FS. Data simulation was repeated for different MSG numbers (range, 2-7). Higher reproducibility was noted for every unit increase in MSG number, with the median absolute difference between 2 within-patient FS measurements decreasing from 1.05 (SD = 0.25) with 2 glands to 0.52 (SD = 0.12) with 7 glands. MSG number influenced the probability of a simulated patient receiving a FS ≥1, increasing from a median of 0.67 with 2 glands to 0.77 with ≥5 glands. MSG number influenced clinical trial sample sizes. For example, 80% statistical power to detect a 40% FS reduction required a sample size per group of 62 with 2 glands and 25 with 7 glands. For a diagnostic threshold of FS ≥1, a minimum of 5 glands should ideally be targeted. For continuous FS values, a larger number of MSGs (eg, 6) will increase reproducibility further and reduce clinical trial sample size requirements.