Refer to answer. Psoriatic spondylitis refers to inflammation of the sacro-iliac joints and the spine and is one manifestation of psoriatic arthritis. The primary symptoms are chronic low back pain and stiffness. Hip involvement can also be seen. It is one form of what are known as spondyloarthropathies, which include anklylosing spondylitis, reactive arthrtis, arthritis with inflammatory bowel disease, etc.
Spondylitis. Auto immune inflamatory disorder of spine associated with psoriasis called arthritis when it involves other joints spondylitis when it involves the spine.