We retrospectively reviewed all patients diagnosed with DD presenting to our outpatient clinic for whom serum vitamin D levels were measured from 2011 to 2019. We excluded patients treated with osteoporosis medication and/or calcium/vitamin D supplementation and those diagnosed with a disease influencing mineral metabolism such as chronic kidney disease, hyperparathyroidism, and liver disease. We excluded diabetic patients as low vitamin D status has been suggested to be associated with increased risk of developing type 1 or type 2 diabetes [14, 15]. Women were excluded due to an insufficient number for statistical analysis. A total of 32 men (mean age 69.6, range 58–80) with DD were recruited as cases.
For healthy control patients, we obtained the data of asymptomatic men who participated in the early medical diagnosis and disease prevention program at our institution’s health care center over the same period. Among the 3,014 men, 64 age-matched healthy subjects (mean age 68.8, range 60–80) were recruited as controls for a 1:2 ratio.
From the case group, diseased palmar fascia samples were obtained from 14 patients undergoing open fasciectomy for DD. Four of the patients were being treated for a recurrence of the disease after having undergone a previous operation at another institution. All samples were collected with the written informed consent of the patient. The excised tissue was obtained for study under a protocol which was approved by the hospital Institutional Review Board (No. B-1606/352 − 304). Samples were allocated for vitamin D receptor and TGF-β1 immunohistochemistry
Measurement of serum vitamin D levels
Serum 25(OH)D (25-hydroxyvitamin D) levels were measured in all DD patients and as one of the routine lab examinations for controls. We used Diels-Alder derivatization and ultrahigh-performance liquid chromatography-tandem mass spectrometry (Waters, Milford, MA, USA) for measurement, which is the reference standard for 25(OH)D measurement [16]. Vitamin D levels were categorized as deficient (< 20 ng/mL) and non-deficient(≥20 ng/mL).
Evaluation of clinical features of DD
Clinical parameters including age, body mass index, duration of symptoms, bilateral hand involvement, past surgical history of the affected hand, age at disease onset, and total extension deficit at involved metacarpophalangeal(MP), proximal interphalangeal(PIP) and distal interphalangeal(DIP) joints were investigated.
We used the classification of Iselin [17] to assess the severity of the disease. This classification consists of four categories (Table 1).
Table 1
Staging of Dupytren’s disease according to the Iselin classification. Expressed by the grade of the worst affected finger.
Grade | Deformity |
I | Palmar nodules and small cords without signs of contracture |
II | Contracture of the MP joint |
III | Contracture of the MP and PIP joint |
IV | Severe contracture of the MP and PIP joint with hyperextension deformity of the distal interphalangeal (DIP) joint |
Finger involvement was also classified according to Tubiana’s staging [18] (Table 2).
Table 2
Staging of Dupytren’s disease according to the Tubiana classification.
Stage | Deformity |
0 | No lesion |
N | Nodular presence without finger contraction |
1 | Total extension deficit between 0°and 45° |
2 | Total extension deficit between 45°and 90° |
3 | Total extension deficit between 90°and 135° |
4 | Total extension deficit superior to 135° |
Total passive extension deficit of each involved finger is calculated using a goniometer adding the extension deficit at MP, PIP, and DIP joints. For scoring purposes, the nodular stage (N) is graded at 0.5 point. The number of each other stage determines the points, e.g. stage 2 scores 2 points.
Sample preparation
After surgical removal of diseased palmar fascia in 14 patients, the tissue samples were fixed in 10% buffered formalin, embedded in paraffin, and sliced into 4-mm-thick blocks of tissue. 4-um-thick sections cut from these blocks underwent further staining to assess the histological features.
Immunohistochemical analysis
All immunohistochemical stains were performed on a Ventana BenchMark XT (Ventana Medical Systems, Tucson, AZ, USA) automated stainer.
Deparaffinized, 4-um-thick sections were mounted on charged slides. Antigen retrieval was achieved using a tris-based buffer, pH 8.4, (Cell Conditioning Solution CC1, Ventana Medical Systems) held at 100 °C for 24 minutes. 3% hydrogen peroxide (H2O2) was used to block endogenous peroxidase activity at 37 °C for 4 minutes.
Tissue sections were then incubated with rabbit polyclonal vitamin D receptor antibody (Cloud-Clone, product number PAA475Hu01, 1:500) or rabbit polyclonal TGF-beta1 antibody (Cloud-Clone, product number PAA124Hu01, 1:200) at 37 °C for 16 minutes.
Antigen-antibody reactions were then observed using the Ventana OptiView DAB IHC Detection Kit according to the manufacturer's recommendations. OptiView HQ Universal Linker, which has numerous non-endogenous HQ haptens, binds the primary antibody. HRP multimer binds to the HQ haptens. The number of multimer molecules is multiplied in this way, resulting in increased staining intensity without increased background. DAB chromogen reacts with HRP and H2O2 to generate a clean, crisp signal.
Counterstaining was performed on the Ventana Benchmark XT using hematoxylin II for 8 minutes, followed by bluing reagent for 4 minutes.
The assessment of the degree of staining and distribution patterns of specific immunohistochemical staining were evaluated using a semi-quantitative assay as used for steroid receptors [19, 20]. The staining index (SI) was calculated by multiplication of the staining intensity and percentage of stained cells. Staining intensity was classified as follows: 0 = negative, 1 = weak, 2 = moderate, and 3 = strong staining. The percentage of positively stained cells was scored as follows: 0 = no staining, 1 = < 10% of cells, 2 = 11–50% of cells, 3 = 51–80% of cells, and 4 = > 81% of cells stained (Fig. 1). The total SI per sample therefore ranged from 0 to 12; 0 to 1 indicates no staining (e.g., negative results), 2 to 4 indicates moderate staining, and 6 to 12 indicates high staining. This evaluation was based on the original Remmele and Stegner characterization for hormone receptors in breast cancer [21].
Figure 1. Representative cases showing varying degree of VDR staining index: (a) negative (b) weak (c) moderate (d) strong.
Statistical analysis
We compared vitamin D levels between the DD group and the healthy control group using an independent samples t-test.
We divided our case population into two groups; vitamin D deficient (< 20 ng/mL) and vitamin D non-deficient(≥20 ng/mL). We compared clinical characteristics between the two groups using an independent samples t-test for age, duration of symptoms, and body mass index (BMI). A Mann-Whitney U test was used for total extension deficit, Iselin staging, Tubiana total staging, and Tubiana staging for the worst affected finger. Pearson’s chi-square test was run for early onset of disease and Fisher’s exact tests were run for bilateral hand involvement and past surgical history of the affected hand.
Correlations between vitamin D levels and VDR, TGF-β1 expression levels in collected palmar fascia samples were evaluated using the Spearman’s rank correlation test.
All statistical analyses were performed using the SPSS software package (version 22.0; SPSS Inc., Chicago, IL, USA). A p-value of less than 0.05 was considered statistically significant.