Psoriatic arthritis is a painful, inflammatory condition of the joints that can affect up to 30 percent of patients with psoriasis. It has an incidence of approximately 6 per 100,000 per year and a prevalence of about 1–2 per 1,000 in the general population. Among patients with psoriasis, the prevalence of psoriatic arthritis ranges between 4 and 30 percent. In most cases, arthritis appears 10 years after the first signs of skin psoriasis, usually between the ages of 30 and 50. However, in approximately 13–17% of cases, arthritis precedes the skin disease. Both men and women are equally affected by psoriatic arthritis, which is a lifelong condition that usually progresses over time, with symptoms that come and go.

Patients with psoriasis who are more likely to develop arthritis include those with psoriatic nail disease, flexural psoriasis, scalp psoriasis, post-auricular psoriasis, obesity, smoking habits, and elevated baseline C-reactive protein (CRP). Psoriatic arthritis is classified as a form of spondyloarthritis, a family of disorders that also includes ankylosing spondylitis, non-radiographic axial spondyloarthritis, reactive arthritis, enteropathic arthritis, and undifferentiated spondyloarthritis. These conditions share several clinical features such as axial joint inflammation, asymmetric oligoarthritis, dactylitis, enthesitis, negative rheumatoid factor, HLA-B27 positivity, genetic susceptibility, and distinctive radiological features.

The development of psoriatic arthritis is influenced by genetic predisposition, immune factors, and environmental factors. A genetic predisposition is evident as many patients with psoriatic arthritis have a familial tendency toward the condition. Immune factors play a role, with an overactive immune system and increased inflammatory markers observed in patients. Environmental factors implicated in the pathogenesis include infections, trauma, recurrent oral ulcers, obesity, and bone fractures.

The signs and symptoms of psoriatic arthritis include joint pain, swelling, and stiffness, with five main patterns of joint involvement: distal arthritis, asymmetric oligoarthritis, symmetric polyarthritis, spondyloarthritis, and arthritis mutilans. Psoriatic nail disease, which includes features like nail pits, onycholysis, distal nail bed hyperkeratosis, and splinter haemorrhages, occurs in 90% of patients with psoriatic arthritis. Other features include enthesitis, dactylitis, fatigue, and mouth ulcers. Psoriatic arthritis is also associated with co-morbidities such as ocular involvement, cardiovascular disease, inflammatory bowel disease, metabolic syndrome, hypertension, diabetes, atherosclerosis, and mental health issues.

Psoriatic arthritis is typically diagnosed based on symptoms, examination of skin and joints, and compatible X-ray findings. There are no specific diagnostic blood tests, but markers of inflammation and genetic testing may support the diagnosis. Treatment for psoriatic arthritis often involves a stepwise approach, starting with non-pharmacological strategies and progressing to pharmacological treatments if necessary. Early and aggressive treatment is recommended to prevent joint deformity and resulting morbidity. Non-pharmacological management includes physical and occupational therapy, exercise, orthotics, and education. Pharmacological treatment options range from non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroid injections to disease-modifying antirheumatic drugs (DMARDs) and biological DMARDs such as TNF-alpha inhibitors.

The long-term prognosis for psoriatic arthritis varies, with most patients experiencing ongoing issues with arthritis throughout their life. Remissions are uncommon, and those with severe psoriatic arthritis may have a shorter lifespan than average. Factors associated with a good prognosis include male sex, fewer joints involved, good functional status at presentation, and previous remission in symptoms. Conversely, a poor prognosis is associated with elevated ESR or CRP at presentation, failure of previous medication trials, absence of nail changes, joint damage, and certain genetic markers.

In conclusion, psoriatic arthritis is a complex and chronic condition that requires comprehensive management and treatment strategies to improve patient outcomes and quality of life.