Psoriatic arthritis and magnetic resonance imaging.

Sir, We read with interest the article by Of®dani et al. entitled ``Subclinical joint involvement in psoriasis: magnetic resonance imaging and X-ray ®ndings'' (1). Psoriatic arthritis (PA) is an in ̄ammatory arthropathy occurring in 5 ± 7% of patients with psoriasis. Several distinct pattern of PA are present, namely: oligoartriculer, arthritis mutilans, symmetric and asymmetric polyarthritis, and psoriatic spondiloarthritis. The interphalangeal joints of the ®ngers and toes are most commonly affected (2,3). In the study by Of®dani et al., arthritic signs in the magnetic resonance imaging (MRI) of the hands of 25 psoriatic patients without any joint symptoms and signs are described. The clinical impact of these ®ndings is not clear. Are these signs really early manifestation of articular involvement? A follow-up period and a control MRI of the patients will be more informative and may show the place of MRI for the early prediction of a future clinically apparent articular involvement. Since approximately 5% of patients develop severe disabling and deforming arthritis during the course of PA, more aggressive treatment can be instituted in the selected patients. The classic radiographic features of PA are destructive lesions involving the distal and proximal interphalangeal joints of the ®ngers and the toes, periostitis of the large joints, pencil-in-cup appearance and absence of symmetry (4). It would also be more appropriate to include patients with clinically apparent PA as well, so correlation between the early and established sign of PA in MRI would be possible. Although the authors suggest that skin and nail psoriatic involvement cannot be regarded as an indicator or predictable diagnostic marker of PA, PA usually follows wellestablished cutaneous or nail lesions and constitutional symptoms, such as malaise, morning stiffness and fever, can be present. A search for an association between clinical and laboratory activation markers, i.e. sedimentation rate and other acute-phase reactants, and MRI ®ndings would be appropriate. MRI is an expensive method and the therapeutic and prognostic implications in psoriasis are not clear. It is also a highly sensitive method and false positive results are not rare. Thus, further study is necessary to determine the place of MRI in the diagnosis of PA.