The primary aim of the study is to assess the effect of methotrexate on the development of distal interphalangeal joint extensor tendon enthesopathy.

Nail psoriasis is one of the risk factors for psoriatic arthritis (PsA), especially with distal interphalangeal joints affected. Nail changes in psoriasis have been observed in 10-55% of patients, and the nail psoriasis-related inflammation can spread to adjacent structures, including DIP joints and digital extensor tendons. Enthesopathies are among the characteristic features of psoriatic arthritis. In everyday practice, assessment of psoriatic changes in nails is based mainly on clinical indices, such as nail psoriasis severity index (NAPSI) and modified NAPSI (mNAPSI), while imaging examinations, such as ultrasonography are performed much less frequently.

The findings of this study may assess the reasonableness of systemic treatment of nail psoriasis in patients without arthritis as enthesopathy prevention as well as the usability of US nail examinations in Ps and PsA patients in assessment of morphological changes and a response to treatment.

A US examination of nails and distal interphalangeal joint extensor tendons are conducted in all of the patients twice at an interval of six months. The examination is conducted by a rheumatologist experienced in ultrasound examinations of the skeletal and muscular system. An assessment of the nails, extensor tendons and DIP joints is made by placing the head on the dorsal side. In order to avoid pressure on surface tissues, an appropriate amount of gel without gel pads was used. The intensified blood flow, made visible by the PD technique, is confirmed by pulsed wave Doppler spectrum. The nail thickness is measured as the maximum distance between the dorsal and ventral nail plates. The nail bed thickness is measured as the distance between the ventral plate and the bone margin of the distal phalanx. The nail matrix thickness is measured at the proximal end of the nail bed.

The study was approved by the Bioethics Committee of the Warmia and Mazury Chamber of Physicians The study are conducted according to the Good Clinical Practice guidelines. Each participant signs an informed consent and be coded with unique ID.

Results of analyses will be saved by indexing with ID code only, personal data with individual IDs will be saved in additional file. All hard copy will be archived in secure room with coded electronic key.

Inclusion Criteria:

• Patients with psoriatic changes in nails treated at the Rheumatological Clinic in Olsztyn and the Clinic of Dermatology, Sexually Transmitted Diseases and Clinical Immunology of the University of Warmia and Mazury in Olsztyn, in whom a US examination revealed DIP joint extensor tendon enthesopathy

Exclusion Criteria:

• Patients diagnosed with osteoarthritis of hands, those who work hard physically and those with changes in nails other than caused by psoriasis

Patients with psoriatic changes in nails with distal interphalangeal extensor tendon enthesopathy in ultrasound examination