Background: Tocilizumab has been proved to be an alternative to corticosteroids in treating polymyalgia rheumatica. Considering the action on interleukin-6 on bone turnover an effect of tocilizumab is supposed. Few data are available about bone turnover in rheumatoid arthritis patients treated with tocilizumab but no data are available in polymyalgia rheumatica patients.

Objectives: This study explores changes in the bone homeostasis by testing the N-terminal collagen type I extension propeptide (PINP) marker for osteo-formation and the carboxy-terminal region of collagen type I (CTX-I) marker for osteo-resorption in patients taking tocilizumab for polymyalgia rheumatica (PMR).

Methods: Twenty patients were included in the prospective open-label TENOR study (Clinicaltrials.gov NCT01713842) and received three monthly tocilizumab infusions, followed by corticosteroids starting at week (W)12. PINP and CTX-I were tested at inclusion (W0), after tocilizumab but before steroid initiation (W12), at the end of the protocol (W24) and were compared to healthy controls. Information regarding disease activity, inflammatory parameters and interleukin (IL)-6 levels were collected during the follow-up of the patients.

Results: Polymyalgia rheumatica patients were characterized by higher levels of CTX-I relative to healthy controls matched in age and sex at baseline. PINP levels increased at W12 ( p =0.0008 , versus W0) following tocilizumab introduction and CTX-I levels decreased at W24 and after steroid initiation ( p =0.001 , versus W0) ( figure 1 ). Such modifications explain the altered correlation observed between PINP and CTX-I at W0 (r=0.255 at W0 versus r=0.641 in healthy controls) and its correction after treatment (r=0.760 at W12 and r=0.767 at W24). Finally, greater changes in PINP were observed in patients whose circulating IL-6 levels decreased after tocilizumab therapy.

Figure 1

Evolution of PINP (A) and CTX-I (B) in polymyalgia rheumatica patients under tocilizumab therapy (W0-W12) and under corticosteroids (W12-W24). Correlation between CTX-I and PINP in polymyalgia rheumatica patients at week 12 (C) and 24 (D)

Conclusion: Control of bone turnover, in part through the inhibition of the IL-6 axis, is observed during tocilizumab and subsequent steroid treatment of polymyalgia rheumatica.

Disclosure of Interests: Guillermo CARVAJAL ALEGRIA: None declared, Eleonore Bettacchioli: None declared, Alain Saraux Consultant for: Roche SAS, Speakers bureau: Chugai Pharma France, Divi Cornec: None declared, Valerie Devauchelle-Pensec Grant/research support from: Roche-Chugai, Speakers bureau: MSD, BMS, UCB, Roche, Yves Renaudineau: None declared

DOI: 10.1136/annrheumdis-2019-eular.4539