A 36-year-old man presents with seronegative inflammatory arthritis (anti-CCP and rheumatoid factor negative) predominantly affecting the knees and the DIPJs. There is no past or family history of psoriasis. Which of the following is true about psoriatic arthritis?

a. Site of psoriasis involvement increases the risk of psoriatic arthritis
b. Nail pitting and onycholysis do not associate with arthritis
c. Over 60% of psoriasis patients develop inflammatory arthritis
d. Psoriatic arthritis may precede skin involvement in 15-25% of cases
e. Severity of skin involvement increases the risk of psoriatic arthritis