Myklebust 1986.

Methods	Design: RCT Number of centres: 9 Treatment duration: 12 weeks Flare design: No Wash‐out period: Yes (1 week) Time point of assessments: BL, 4, 8, 12 weeks
Participants	Inclusion criteria: 1. Between 18 and 80 years of age, with Bechterew syndrome; 2. Disease duration of more than six months. Exclusion criteria: None reported. Classification: NA Naproxen (1000 mg): Number of participants: 21 Number of completers: NA Age (mean (SE)): 41.5 (2.3) Male (%): 57 Symptom duration: NA Disease duration: NA HLA‐B27 positive (%): NA Piroxicam (20 mg): Number of participants: 16 Number of completers: NA Age (mean (SE)): 41.7 (4.0) Male (%): 63 Symptom duration: NA Disease duration: NA HLA‐B27 positive (%): NA
Interventions	Naproxen (1000 mg) vs Piroxicam (20 mg) Co‐medication: Antimalarial drugs, penicillamines or gold were allowed if treatment had lasted more than 6 months, as well as low dose corticosteroids.
Outcomes	Extracted outcomes: 1. Pain on VAS 2. Duration of morning stiffness (BL (median ± IQR), post‐treatment after 12 weeks (median ± IQR)) (in minutes, higher is worse) Naproxen 1000 mg: 210 ± 120 to 300 (N = 19), 90 ± 30 to 150 (N = 19) Piroxicam 20 mg: 120 ± 60 to 180 (N = 16), 60 ± 15 to 172.5 (N = 16) 3. Chest expansion (BL (± SE), percentage change after 12 weeks (± SE)) (in cm, higher is better) Naproxen 1000 mg: 4.9 ± 0.6 (N = 19), +28.8% ± 8.9% (N = 19) Piroxicam 20 mg: 4.1 ± 0.4 (N = 16), +22.2% ± 7.9% (N = 16) 4. Schober's test (BL (± SE)), percentage change after 12 weeks (± SE)) (in cm, higher is better) Naproxen 1000 mg: 3.0 ± 0.2 (N = 19), +13.1% ± 8.9% (N = 19) Piroxicam 20 mg: 2.6 ± 0.2 (N = 16), +59.2% ± 34.7% (N = 16)
Notes	Outcomes that were not included in the meta‐analysis, because they could not be extracted due to the presentation of these outcomes: duration of morning stiffness, chest expansion, Schober's test. Available results are described in this table. Adverse events were not reported separately for patients with rheumatoid arthritis and AS, and could therefore not be used. Funding source: Not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No information was provided on sequence generation.
Allocation concealment (selection bias)	Unclear risk	No information was provided on allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	A double dummy technique was used for adequate blinding of participants.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No further information provided on blinding of outcome assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Overall dropout rates are low (n = 12, 11%) and mainly concerned participants with RA.
Selective reporting (reporting bias)	Low risk	All outcomes stated in the methods are reported.
Other bias	Unclear risk	BL characteristics imbalance cannot be determined. No information is provided on the statistical methods that were used.