The study is an open intervention study with the aim to determine the effects of weight-loss treatment with Low-Energy liquid Diet (LED) on disease activity, quality of life and markers of the metabolic syndrome in patients with psoriatic arthritis and obesity.

BACKGROUND Psoriasis is a common skin disease affecting around 2-3% of the population in Sweden. Approximately 20-30% of the individuals with psoriasis develop psoriatic arthritis (PsA). PsA mainly engage the musculoskeletal apparatus and causes inflammation of joints, tendons and ligaments, but the disease also increases the risk of developing anterior uveitis and inflammatory bowel disease, especially Crohn's disease.

Both psoriasis and PsA are strongly associated with obesity and the metabolic syndrome (Mets). Observational studies have reported a frequency of obesity (body mass index; BMI≥30 kg/m2) in 45% and of MetS in 30-45% of PsA patients. Earlier studies have shown that obesity increases the risk of developing both psoriasis and PsA and that obesity is associated with increased disease activity, poorer treatment response and lower chance of achieving minimal disease activity.

Although the association between PsA and obesity is well known, there are only a small number of interventional studies which have assessed the effects of weight loss on disease activity in PsA.

Patients with PsA also have an increased risk of cardiovascular disease. [12, 13] Chronic inflammation, which accelerates the atherosclerotic process, in combination with a higher prevalence of cardiovascular risk factors among PsA patients is believed to contribute to this increased risk.

Obesity causes a low grade systemic inflammation via the production of pro-inflammatory mediators in the white adipose tissue, such as adipokines and cytokines (e.g. tumour necrosis factor-α and interleukin-6), which are also involved in the pathogenic process if PsA. Obesity-related inflammation could thus act synergistically with autoimmune inflammation in the development and the maintenance of disease in psoriasis and PsA.

Weight-loss treatment with Very Low Energy Diet (VLED) is an effective and approved method in clinical use in Sweden. In severe obesity, BMI 35 kg/m2 or more, a strict energy restriction is needed for optimal weight-loss. The LED gives a daily intake of 640 calories together with the recommended doses of vitamins and minerals. During an initial period of 12 weeks the patients only consume LED. The weight-loss with this intake is 1-2 kilograms per weeks. After the strict period food is successively reintroduced during a period of 18 weeks. The treatment is given within the framework of a structured program including support and medical follow-up from a team of doctors, nurses and dieticians.

AIMS The aims of this study are

• To determine the effects of weight loss treatment on disease activity, function, quality of life and markers for the metabolic syndrome in patients with psoriatic arthritis
• To study the specific effects on the immune system of the negative energy balance during the strict energy restriction period and prospectively, during a two year follow-up
• To investigate if there are differences in body-composition, markers for Mets and adipokines between patients with PsA and obesity and controls with obesity before during and after weight loss treatment.

PATIENTS AND METHODS Patients with PsA and obesity registered at the Rheumatology clinics of Sahlgrenska University hospital and the hospitals of Alingsås and Borås are invited to participate.

The results of the PsA patients will be compared with control patients with obesity (PsA or psoriasis) matched for age, sex and BMI who undergo the same weight loss treatment with VLED.

Disease activity, physical function and quality of life will be assessed by physical examination (including anthropometric measures, joints, tendons, back mobility and skin) and by validated questionnaires at baseline (start of weight-loss treatment), 3 months, 6 months, 12 months and 24 months. Blood samples will be collected at the same appointments.

Body-composition will be measured at baseline and 12 months. Muscle strengths and physical function will be measured at baseline, 6 months and 12 months and physical activity will be assessed with questionnaires and accelerometers.

Informed written consent will be obtained from all patients and controls. The study was approved by the local regional ethics committee in Gothenburg and will be carried out in accordance with the Helsinki Declaration.

Inclusion Criteria:

• PsA fulfilling the Classification for Psoriatic Arthritis (CASPAR) criteria
• BMI≥33 kg/m2
• Age 18-75 years

Exclusion Criteria:

• Pregnancy
• Porphyria
• Epilepsy
• Diabetes type 1
• Severe heart or kidney disease
• Eating disorder
• Severe catabolic disease