Introduction

• Psoriatic arthritis (PsA) affects up to 1%^1,2 of the population. The proportion of patients with skin psoriasis who develop PsA is uncertain, with estimates ranging from 6% to 42%,^1,3,4 usually within 5–10 years of cutaneous disease onset¹
• Patients with psoriasis or PsA, or both, generally have reduced health-related quality of life, productivity and functionality¹
• Approximately two-thirds of patients with PsA develop joint damage;⁵ joint erosions develop within 2 years of PsA symptom onset in approximately 50% of patients⁴
• The presence of PsA and psoriasis adds approximately US $23,000/year (approximately €20,000) to the total medical costs versus patients without PsA and psoriasis⁶

Differences between PsA and rheumatoid arthritis

Despite apparent similarities between PsA and rheumatoid arthritis, there are important differences between them⁷

	Psoriatic arthritis	Rheumatoid arthritis
Clinical/anatomical	DIP joint and axial arthritis Often asymmetrical Enthesitis common	MCP and wrist joints Predominantly symmetrical
Genetic	HLA Cw6 and B27 IL23 receptor	HLA DRB1
Pathogenesis	Absence of circulating autoantibodies Distinct vascular pathology T-lymphocyte predominance Early expression of vascular growth factors	Circulating autoantibodies RF/ACPA T-lymphocyte and B-lymphocyte infliltrate Late expression of vascular growth factors
Response to therapy	DMARDs, e.g. MTX TNF inhibitors Abatacept Ustekinumab Secukinumab	DMARDs, e.g. MTX TNF inhibitors Abatacept Rituximab Tocilizumab

ACPA, anti-citrullinated protein antibody; DIP, distal interphalangeal; DMARDs, disease modifying anti-rheumatic drugs; HLA, human leukocyte antigen; MCP, metacarpophalangeal; MTX, methotrexate; RF; rheumatoid factor; TNF, tumor necrosis factor.

Adapted from Veale and Fearon.⁷

Burden of psa

PsA: Under-diagnosis and under-treatment

• PsA may be underdiagnosed,⁸ and if untreated it can lead to severe disability and comorbidities⁹
• An international survey (712 PsA patients) found that more than half of patients (59%) reported that they were receiving no treatment or receiving topical therapy only, and were not receiving any systemic medication for their joint disease¹⁰

Adapted from Kavanaugh et al.¹⁰ A total of 712 patients with PsA were included. ^*Including only patients with PsA who reported joint pain (n=628).

Impact

Adapted from Kavanaugh et al.¹⁰ Shown are the proportions of patients who responded ‘with much difficulty’ or ‘unable to do’.

Adapted from Kavanaugh et al.¹⁰ Shown for ‘Missed work in past 12 months’ is the proportion of patients who responded with ‘yes’; all other responses represent the proportion of patients reporting ‘a lot’ or ‘some’ impact of PsA.

Treatment

Treatment options in PsA

Treatment	Comments
NSAIDs	Still widely used for PsA treatment, especially in mild disease Can relieve musculoskeletal symptoms, but have no efficacy on skin lesions Milder/less toxic than DMARDs
Steroids	Local injections of steroids can be used as adjunctive therapy for peripheral arthritis and enthesitis Systemic steroids can lead to flares of skin psoriasis, so should be used with caution
Conventional DMARDs	Patients with active disease despite NSAID therapy should receive DMARDs They are ineffective in axial disease, and little evidence of efficacy in enthesitis Methotrexate (MTX) MTX is recommended in guidelines as the first choice DMARD, either as monotherapy or in combination Sulfasalazine May improve peripheral arthritis and functional outcomes No evidence that it can inhibit progression of joint damage Leflunomide May improve joint and skin symptoms in PsA The combination of leflunomide and MTX is associated with elevated liver function tests and so should be monitored carefully Cyclosporine and tacrolimus May be effective for the treatment of peripheral arthritis, axial involvement and skin lesions Adverse events include renal toxicity and hypertension, which requires careful monitoring
Biologics	TNF inhibitors Can improve signs and symptoms of inflammation in both peripheral and axial joints as well as in peri-articular tissues such as enthuses Can also improve functional status, quality of life, and skin and nail manifestations of PsA Can slow the progression of damage in peripheral joints Options include etanercept, infliximab, adalimumab, golimumab, and certolizumab pegol IL-12/23 inhibitor (ustekinumab) Evidence of efficacy in PsA in terms of ACR20 and ACR50 responses, and evidence of slowed radiographic progression IL-17 inhibitor (secukinumab)
Small molecular weight inhibitors	Phosphodiesterase inhibitor (apremilast) Downregulates the inflammatory response Has been shown to be effective in PsA, improving signs, symptoms and physical function

DMARDs, disease-modifying anti-rheumatic drugs; NSAID, non-steroidal anti-inflammatory drug. Adapted from Kang and Kavanaugh.¹¹

Guidelines

Grappa guidelines

The Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) guidelines place equal emphasis on the dermatological and rheumatological aspects of PsA.

Adapted from Ritchlin et al.¹²

EULAR guidelines

Unlike GRAPPA, the EULAR guidelines put the primary emphasis on the musculoskeletal aspects of the disease.¹³

EULAR treatment guidelines¹³

Adapted from Gossec et al.¹³ CsA, ciclosporin A; csDMARD, conventional systemic disease-modifying anti-rheumatic drug; LEF, leflunomide; SSZ, sulphasalazine; TNF, tumour necrosis factor.

Support

Additional information

You can find additional information about PsA by following these links:

NHS Choices:
http://www.nhs.uk/conditions/psoriatic-arthritis/Pages/Introduction.aspx

National Psoriasis Association:
https://www.psoriasis.org/psoriatic-arthritis

Psoriasis and Psoriatic Arthritis Alliance:
http://www.papaa.org/resources/about-psoriasis