Investigators hypothesize that TNFi is superior to SC MTX in preventing structural damage in early, treatment-naïve PsA, assessed using HR-pQCT. The study aims to ascertain:

- The effect of SC MTX and TNFi (adalimumab biosimilar) on erosion and enthesiophyte progression in early PsA by HR-pQCT.

Participants will be:

• Randomized in a 1:1 ratio to either the SC MTX group or the TNFi group.
• HR-pQCT of MCPJ 2-4 will be performed at baseline, week 24, and one year.

The primary outcome is the comparison of change in erosion volume over MCPJ 2-4 across 48 weeks between the SC MTX group (group 1) and the TNFi group (group 2), assessed by HR-pQCT.

Inclusion Criteria:

• ≥18 years old
• without severe deformity in MCPJ
• with active disease, which is defined as ≥1 tender joints and ≥1 swollen joints, despite previous treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) for ≥ 4 weeks
• with at least one poor prognostic factor (eg, polyarthritis, structural damage on HR-pQCT or CR, elevated acute phase reactants, dactylitis, nail involvement or HAQ-DI>1)
• symptom duration ≤ 2 years

Exclusion Criteria:

• on csDMARDs unless being prescribed for skin psoriasis (e.g. cyclosporin)
• limited in ability to perform usual self-care, vocational, and avocational activities
• pregnancy
• previous therapy with b/tsDMARDs
• predominant active axial PsA or significant uveitis/inflammatory bowel disease requiring immediate b/tsDMARDs therapy
• the presence of active inflammatory diseases other than PsA
• active infection in 2 weeks before randomization or a history of ongoing, chronic, or recurrent infections including tuberculosis
• history of malignant disease within the past 5 years (excluding basal cell carcinoma or actinic keratosis, in-situ cervical cancer, or non-invasive malignant colon polyps)
• contraindications to MTX or adalimumab