Which skin disorder affects primarily the limbs with crusted lesions?

The skin disorder that affects primarily the limbs with crusted lesions is psoriasis. Psoriasis is characterized by red patches covered with thick, silvery scales and can indeed present with lesions that have a crusted appearance. It commonly occurs on extensor surfaces like elbows and knees but can be found on any part of the body.

Moreover, the relationship between psoriasis and the formation of crusted lesions is particularly notable, as the rapid skin cell turnover leads to the buildup of skin cells. This condition can also affect the nails and joints, making it a systemic issue rather than just a localized skin problem.

In contrast, scabies is caused by a parasitic infestation that can lead to irritation and itching but does not typically produce crusted lesions in a localized manner on the limbs. Ringworm, a fungal infection, also does not primarily cause crusted lesions, rather it typically presents as ring-shaped, red patches with clearer centers. Eczema is an inflammatory skin condition that causes dryness, redness, and itching, but it does not generally result in crusted lesions as seen in psoriasis.