Unsuppressed parathyroid hormone in patients with autoimmune/inflammatory rheumatic diseases: implications for vitamin D supplementation.
OBJECTIVE
To verify if autoimmune/inflammatory rheumatic disease (ARD) patients were more refractory to PTH suppression by 25(OH) vitamin D (VITD).


METHODS
Data from 105 consecutive ARD patients (including RA, PMR, spondyloarthritis and other CTDs) attending a tertiary-level immuno-rheumatology clinic and 1542 subjects tested at our central laboratory from 2008 to 2010 (controls) were collected. After exclusion of patients with renal failure, primary hyperparathyroidism and hypercalcaemia (n = 522), plasma VITD, PTH, calcium and phosphate concentrations were compared between these two groups.


RESULTS
Plasma VITD concentrations were <25 nmol/l in 257 patients (severe deficit, 22.8%), ≥25 nmol/l but <75 nmol/l in 661 (mild deficit, 58.8%) and ≥ 75 nmol/l in 207 (normal, 18.4%). Despite similar median age, plasma VITD, calcium and phosphate values (P = 0.96, 0.30, 0.94, respectively), PTH was higher in ARD {73.0 [interquartile range (IQR) 54.2-93.7] pg/ml} than in controls [61.4 (46.9-80.3), P < 0.0002], also in all above-defined VITD categories (P < 0.05). Suppressed PTH was observed in 96.9% (95% CI 95.8%, 98.0%) of controls with VITD ≥ 75 nmol/l. However, PTH was increased more frequently in ARD vs controls. At multiple linear regression analysis, plasma VITD, age and the presence of an ARD (partial correlation coefficients -0.21, 0.15, 0.12, respectively, P < 0.0001) were independent predictors for increased PTH.


CONCLUSIONS
Patients with ARD had, on average, an increased PTH concentration for any plasma VITD range, suggesting an impaired vitamin D metabolism. Therefore, vitamin D supplementation to ARD patients may be targeted to reach PTH suppression and not simply to obtain VITD concentrations considered optimal in other categories of patients.
Dipartimento di Medicina Clinica e Sperimentale, Via Solaroli 17, Novara, Italy. sainaghi@med.unipmn.it
Pier Paolo
PP
Sainaghi
Mattia
M
Bellan
Giuseppina
G
Antonini
Giorgio
G
Bellomo
Mario
M
Pirisi
D000368:Aged; D001327:Autoimmune Diseases / Q000150:complications* / Q000378:metabolism; D050071:Bone Density Conservation Agents / Q000008:administration & dosage*; D002118:Calcium / Q000097:blood; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010755:Organophosphates / Q000097:blood; D010281:Parathyroid Hormone / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012189:Retrospective Studies; D012216:Rheumatic Diseases / Q000150:complications* / Q000378:metabolism; D012307:Risk Factors; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000150:complications / Q000178:diet therapy*
D050071:Bone Density Conservation Agents; D010755:Organophosphates; D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002118:Calcium