Hospital health professionals perform remote monitoring of frequent patient-reported outcomes, blood test results, and physical activity data available on a digital platform.

Continue using medical treatment with tumour necrosis factor inhibitors (TNFi). Patients will be instructed to use NSAIDs should they experience minor worsening of symptoms, but if the patients experience significant symptom worsening and suspect a severe disease worsening (flare) or adverse events, they will be instructed contact the hospital .

No pre-scheduled visits or remote monitoring.

Continue using medical treatment with tumour necrosis factor inhibitors (TNFi). Patients will be instructed to use NSAIDs should they experience minor worsening of symptoms, but if the patients experience significant symptom worsening and suspect a severe disease worsening (flare) or adverse events, they will be instructed contact the hospital.

Monthly for a subgroup among the Remote monitoring group. ASDAS is a clinical measure of disease activity calculated from four PROs and CRP (or ESR if CRP is not available). The formula for calculating ASDAS CRP = 0.12 × back pain + 0.06 × duration of morning stiffness + 0.11 × patient global + 0.07 × peripheral pain/swelling + 0.58×Ln(CRP + 1)). Higher values indicate worse outcome.

Patient-reported disease activity last 7 days on 6 items using a numeric rating scale (NRS) 0-10. The score is the sum (of the first four individual questions and the mean of questions five and six) divided by five. The sum score range 0-10; higher value indicate worse outcome.

Monthly reported by the Remote monitoring group if disease worsening. Patient-reported disease activity last 7 days on 6 items using a NRS 0-10. The score is the sum (of the first four individual questions and the mean of questions five and six) divided by five. The sum score range 0-10; higher value indicate worse outcome.

Reported every third month by the Patient-initiated care group if disease worsening. Patient-reported disease activity last 7 days on 6 items using a NRS 0-10. The score is the sum (of the first four individual questions and the mean of questions five and six) divided by five. The sum score range 0-10; higher value indicate worse outcome.

Reported monthly by the a subgroup among the Remote monitoring group. Patient-reported disease activity last 7 days on 6 items using a NRS 0-10. The score is the sum (of the first four individual questions and the mean of questions five and six) divided by five. The sum score range 0-10; higher value indicate worse outcome.

CRP measured at home in a subgroup among the Remote monitoring group

Patient-reported disease activity last 7 days on a NRS 0-10 ; higher value indicate worse outcome

Monthly reported by the Remote monitoring group. Patient-reported disease activity last 7 days on a NRS 0-10 ; higher value indicate worse outcome

Reported every third month by the Patient-initiated care group: Patient-reported disease activity last 7 days on a NRS 0-10 ; higher value indicate worse outcome

Patient-reported experience of a significant worsening of symptoms (reflecting a flare in disease activity), response options: no, yes, uncertain. If yes or uncertain, they will be asked which date the flare occurred and the number of days it lasted.

Monthly reported by the Remote monitoring group. Patient-reported experience of a significant worsening of symptoms (reflecting a flare in disease activity), response options: no, yes, uncertain. If yes or uncertain, they will be asked which date the flare occurred and the number of days it lasted.

Reported every third month by the Patient-initiated care group. Patient-reported experience of a significant worsening of symptoms (reflecting a flare in disease activity), response options: no, yes, uncertain. If yes or uncertain, they will be asked which date the flare occurred and the number of days it lasted.

10 item questionnaire (NRS 0-10) used to assess disease activity last 7 days. The score is the sum of each individual question divided by 10, higher value indicate worse outcome.

Item no.6 from Work Productivity and Activity Impairment (WPAI): self-reported activity impairment on a NRS 0-10; higher value indicate worse outcome.

Single item with seven-point response scale ranging from "Much worse" to "Much better".

Single item with seven-point response scale ranging from "Much worse" to "Much better".

Self-reported pain level last 7 days hours on a NRS 0-10; higher value indicate worse outcome.

Self-reported joint pain level last 7 days hours on a NRS 0-10; higher value indicate worse outcome.

1 item from Pittsburgh Sleep Quality Index, self-reported sleep impairment in last month due to pain with 4 response categories ranging "Not during the past month" to "Three or more times a week" ; higher value indicate worse outcome.

1 item with five point response options ranging from "Very satisfied" to "Very dissatisfied", higher value indicate better outcome

Remote monitoring and Patient-initiated care groups, number of steps during daytime captured by wearing a smartwatch

Remote monitoring and Patient-initiated care groups, mean pulse level during daytime captured by wearing a smartwatch

6 item utility instrument for measurement of health related quality of life, 5 first items with 5 response categories, item no.6: self-reported health status on a 0-100 mm scale

Self-reported use of NSAIDs and analgesics and national register data from The Norwegian Prescription Register

For the Control group, examiner assessed metacarpophalangeal (MCP) 1-5, proximal interphalangeal (PIP) 1-5, wrists, elbows, shoulders, ankles, forefeet

At extra visits/withdrawals/early discontinuation in the Remote monitoring and Patient-initiated care groups, For the Control group, examiner assessed MCP 1-5, PIP 1-5, wrists, elbows, shoulders, ankles, forefeet

For the Control group, examiner assessed MCP 1-5, PIP 1-5, wrists, elbows, shoulders, ankles, forefeet

At extra visits/withdrawals/early discontinuation in the Remote monitoring and Patient-initiated care groups, For the Control group, examiner assessed MCP1-5, PIP 1-5, wrists, elbows, shoulders, ankles, forefeet

For the Control group, the presence of heel enthesitis is examined clinically by a health professional. Scored as not present/present right heel/present left heel/present both heels.

At extra visits/withdrawals/early discontinuation in the Remote monitoring and Patient-initiated care groups, , the presence of heel enthesitis is examined clinically by a health professional. Scored as not present/present right heel/present left heel/present both heels.

Self-reported way of transport to the hospital; walking or bicycling/private car/public transportation/taxi/airplane/other.

Self-reported travel distance in kilometres to the hospital.

If in paid work, the need to take time off from work is indicated as yes or no.

Self-reported health care use and national register data on consultations and treatment in secondary and primary health care

Number of extra visits to the hospital or video consultations with a health care provider

Number of withdrawals/early discontinuation

Number of adverse events, serious adverse events, and withdrawals because of adverse events.

Self-efficacy/confidence in using smartphone, tablet, computer, app's, secure login and digital health services. 6 items with Likert scale response categories: Never used, Very bad, Bad, Neither good nor bad, Good, Very good. Score range 1-5; higher scores indicate higher self-efficacy.

20 items from 4 domains of the eHealth Literacy Questionnaire (eHLQ). Four point response scale, sum domain score range 1-4. Lower scores indicate lower eHealth literacy.

To what degree do you understand your body's signs and symptoms. Single item, 4-point Likert scale (not at all - to a large degree + do not know-option)

Service User Technology Acceptability Questionnaire (SUTAQ) reported by the Remote monitoring group. 22 items in 5 subscales. Score range 1-6. Higher scores in subscales 1,2 and 5/lower scores in subscales 3 and 4 indicate higher acceptability with telehealth.

Service User Technology Acceptability Questionnaire (SUTAQ) reported by the Patient-initiated care group. 3 of 22 items: #1, #10 and #11. Score range 1-6. Higher scores in indicate higher acceptability with telehealth.

One item on whether the preferred follow-up strategy would be Remote monitoring or Patient-initated care reported by the two intervention groups only.