Arthrtis of the hand is commonly encountered. Numerous types of arthritis have been investigated and described in order to classify them into non-inflammatory arthritis (osteoarthritis) and inflammatory arthritis caused by crystal deposition (pseudogout, basic calcium phosphate disease, gout), by bacterial and viral infections (Staphylococcus aureus, Neisseria gonorrhea, complications of Lyme disease, Parvovirus, Enterovirus) or by autoimmune processes (RA , PsA , SLE ). Differential diagnosis of hand arthritis is a challenge and represents the optimal medical approach. Certain features must be evaluated in order to make a differentiation. The distribution of synovitis is different in RA (symmetric, great, and small joints including wrist and elbow) than in ankylosing spondylitis (limited to small joints) and psoriatic arthropathy (asymmetric, including toes). Inflammation is more intense in RA than in osteoarthritis. Diagnosis of early seronegative rheumatoid arthritis may be challenging, with consequent possible diagnostic mistakes and inappropriate therapies. This is likely due to the absence of specific markers for seronegative RA, as well as the greater difficulty in classification of RA in early phase. Patients with seronegative RA experienced a delay in diagnosis, according to both the 1987 and 2010 classification criteria, as well as a delay in the initiation of DMARD therapy. Patients with seronegative RA were also less likely to attain remission, suggesting that the window of opportunity for intervention may be more frequently missed in this group. The main differential diagnosis of seronegative forms of early RA is early polyarticular psoriatic arthritis, whose recognition is also troublesome, especially when dealing with minimal or atypical cutaneous or nail lesions

Rheumatoid Arthritis, Psoriatic Arthritis