Cyclophosphamide in Myalgic Encephalopathy/ Chronic Fatigue Syndrome (ME/CFS)

Selfreported Fatigue score is registered every second week, always compared to baseline, as the mean of the four symptoms: "Post-exertional malaise", "Fatigue", "Need for rest", Daily functioning" (scale 0-6, in which 3 is unchanged from baseline). Mean Fatigue scores for the time intervals 0-3, 3-6, 6-9 and 9-12 months are recorded for each patient. Changes in selfreported Fatigue scores from baseline to the mean values in each of the time intervals 0-3, 3-6, 6-9 and 9-12 months follow up, will constitute the primary endpoint.

Responses for the primary endpoint will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

Overall response is recorded as the effect on ME/CFS symptoms during 12 months follow-up. The overall response is not predefined to a specific time interval during follow-up, but is defined as mean Fatigue score at least 4.5 for at least 6 consecutive weeks for moderate response, and mean Fatigue score at least 5.0 for at least 6 consecutive weeks for major response. Single response periods and the sum of response periods during 12 months follow-up will be recorded.

Overall response will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

SF-36 (ver 1.2) is completed by patients at baseline, and at 3, 6, 9, 12 months follow-up. Changes in Physical health summary score, Physical function, and "Mean of five subdimensions" (Physical function, Bodily pain, Vitality, Social function, General health) from baseline to each of the time points 3, 6, 9 and 12 months follow-up are recorded and constitute secondary endpoints. Secondary endpoints will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

The patients' physical activity level, in a home setting for 7 consecutive days, is recorded using Sensewear armbands, with registration at baseline and repeated in the time interval 7-9 months follow-up, and in the interval 11-12 months. Changes from baseline to analysis during the time intervals 7-9 months and 11-12 months, for mean number of steps per 24h, maximum number of steps per 24h, mean duration per 24h with activity level at least 3.5 METs, max duration per 24h with activity level at least 3.5 METs, are recorded. Changes in Physical activity will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

For patients who can tolerate exercise, cardiopulmonary exercise tests will be performed for two consecutive days, at baseline, and repeated in the time intervals 7-9 months, and 11-12 months. A programmed ramp-protocol is used. Oxygen-uptake and work load (Watt) day 2, at maximum effort and at anaerobic threshold, will be recorded and used for comparison to oxygen-uptake and work load with repeated tests after 7-9 and 11-12 months. Changes from baseline to repeated exercise tests after 7-9 and 11-12 months will be analyzed.

Self-recorded "Function level" (scale 0-100, compared to healthy state, according to a set of examples) are registered every second week. Mean "Function level" for the time intervals 0-3, 3-6, 6-9, 9-12 months are calculated. The changes in selfreported "Function level", from baseline to the mean value during each of the the time intervals 0-3, 3-6, 6-9, 9-12 months constitute secondary endpoints.

Changes in Self-reported Function level will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

Fatigue Severity Scale (FSS) is completed by patients at baseline and at 3, 6, 9, 12 months. The changes in FSS from baseline to 3, 6, 9 and 12 months constitute secondary endpoints.

Changes in Fatigue severity scale will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

The longest duration of continuous self-reported Fatigue score ≥ 4,5 (for at least 6 consecutive weeks) within 12 months follow-up.

The longest response duration will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response and for the group with previous rituximab intervention with clinical response but later relapse, and also for all 40 included patients together.

The fraction of patients with sustained clinical response (defined as Fatigue score of at least 4.5) at 12 months, constitute a secondary endpoint.

Sustained clinical response at 12 months will be recorded separately for the group of (at least) 25 ME/CFS patients not given rituximab previously, for the group with previous rituximab intervention for ME/CFS with no clinical response, and for the group with previous rituximab intervention with clinical response but later relapse, and for all included patients together.

Safety will be assessed by interim history, physical examination, and laboratory assessments every four weeks the first six months, thereafter at 6, 9 and 12 months follow-up. Adverse events will be graded according to the Common Toxicity Criteria for Adverse Effects (NCI-CTCAE, version 4.0). Number of patients with any grade, or severe (≥ grade 3 NCI-CTCAE version 4.0) toxicity will be reported, as a measure of tolerability and safety.

Adverse Events may include include hair loss, vomiting, diarrhea, jaundice, leukopenia, anemia, thrombocytopenia, infections, allergic reactions and hemorrhagic cystitis, disturbed ovarian function. The investigators will also collect information on possible toxicity after the formal 12 months study period.