First metatarsophalangeal joint synovial hypertrophy associated with vitamin D status in type 2 diabetes mellitus: An ultrasound-graded study

Abstract

BACKGROUND

The existing semi-quantitative ultrasound grading system inadequately evaluates synovial hypertrophy at the dorsal recess of the first metatarsophalangeal joint (MTPJ). Vitamin D deficiency is prevalent in type 2 diabetes mellitus (T2DM) and may influence joint inflammation. This study hypothesizes that serum 25-hydroxyvitamin D [25(OH)D] levels are inversely associated with synovial hypertrophy severity of the first MTPJ in patients with T2DM.

AIM

To refine ultrasound grading for the first MTPJ synovial hypertrophy and investigate its association with vitamin D in T2DM.

METHODS

This cross-sectional study included 56 patients (112 MTPJs) with T2DM from Shenzhen Traditional Chinese Medicine Hospital. Synovial hypertrophy was evaluated using a refined semi-quantitative ultrasound grading system focusing on the dorsal recess overlying the metatarsal bone. Serum 25(OH)D levels were measured. Logistic regression and threshold analyses assessed associations between vitamin D status and hypertrophy severity.

RESULTS

Of 112 joints assessed, 98 exhibited synovial hypertrophy (grade 1: 40; grade 2: 50; grade 3: 8). The refined grading system demonstrated strong intra- and inter-observer reliability (intraclass correlation coefficients = 0.79 and 0.73, respectively). Lower serum 25(OH)D (< 24.3 ng/mL) was independently associated with moderate-to-severe hypertrophy [odds ratio (OR) = 0.83; P = 0.0163]. Vitamin D deficiency significantly increased the likelihood of moderate-to-severe hypertrophy compared with non-deficiency (OR = 3.86; P = 0.0422). Threshold analysis identified 23.8 ng/mL as a critical serum 25(OH)D level, below which each increment reduced moderate-to-severe hypertrophy risk by 21% (OR = 0.79; P = 0.0078).

CONCLUSION

The refined ultrasound grading system demonstrated strong reliability. Serum 25(OH)D may serve as a protective factor against the severity of synovial hypertrophy in T2DM patients with lower 25(OH)D levels.

Keywords: Vitamin D; Synovial hypertrophy; Type 2 diabetes mellitus; Metatarsophalangeal joint; Serum 25-hydroxyvitamin D

Core Tip: This study refines a semi-quantitative ultrasound grading system for first metatarsophalangeal joint synovial hypertrophy by introducing a novel subtype that specifically classifies cases of dorsal recess overlying the metatarsal bone, demonstrating high reliability (intra-observer intraclass correlation coefficient = 0.79; inter-observer intraclass correlation coefficient = 0.73). We identified a significant inverse, non-linear correlation between serum 25-hydroxyvitamin D levels and synovial hypertrophy severity, with a threshold effect at 23.8 ng/mL. These findings suggest that vitamin D deficiency may contribute to synovial inflammation in type 2 diabetes mellitus patients and that targeted screening and supplementation could help mitigate joint complications.