In the second blog as part of the ‘Know Your Pathology’ series, I will look at Ankylosing Spondylitis (AS). This is a common condition of the vertebral column in which osteophytes develop at the intervertebral space as spurs or as complete bone bridges uniting the vertebral bodies. They develop on the ventral and lateral sides of the vertebral bodies, but may also be found projecting dorsolaterally into the vertebral canal, although these are small and less common. The synovial and cartilaginous joints are affected and erosion and fusion of some of the joints, especially the sacro-iliac joint, occurs; involvement of the sacro-iliac joint is considered to be the hallmark of AS. As the spine fuses, the bodies remodel and their normal shape is lost; the ultimate appearance is smoothing and squaring of the vertebrae or the ‘bamboo spine’.
A progressive, inflammatory disease of unknown aetiology, AS in humans has been associated with the HLA-B27 antigen, found in the blood of up to 95% of Caucasians with the condition. People with AS are at risk from passing the gene to 50 percent of their children; and then the children have a 30 percent risk of developing AS. It affects males predominantly with a male to female ratio of 5: 1, with an age of onset of between 15 to 35 years of age. It is seen commonly in Caucasians and native American populations but rarely in Japanese or African groups.
This condition is common in bulls, pigs and dogs, but is also seen in other species, if less often, and is a disease of some antiquity. It has been described in two crocodiles, one from Egypt and one from Cuba, dating to the Miocene and Pliocene periods respectively. Numerous other prehistoric animals have been described with spinal lesions similar to AS, including the dinosaurs Diplodocus and Polacanthus foxi, the cave bear Ursus spelaeus and the sabre-toothed tiger Smilodon californicus. The mummified remains of animals from Ancient Egypt also show evidence of this condition, whilst descriptions by the fifth century neurologist, Caelius Aurelianus, and Hippocrates also refer to afflictions that could well be AS in humans.
It is possible that many cases of AS in archaeological human populations are not being diagnosed because of the problem of differentiating between AS and Forestier’s disease (also known as Diffuse idiopathic skeletal hyperostosis, or DISH). However, several features can be used to distinguis the two from each other, and from rheumatoid arthritis and psoriatic arthritis. AS has significant erosions of the synovial and cartilaginous joints of the axial skeleton. PA, however, involves the synovial joints of the appendicular skeleton and the cartilaginous joints of the axial skeleton, whereas both promote erosion and repair of the entheses involved. Bony profileration and fusion with no osteoporosis characterises PA and AS, and in RA the cartilaginous joints may or may not be affected. Therefore, if a complete skeleton is available for analysis, it should be possible to differentiate these erosive arthropathies.
This condition has also been reported upon under the following names: spondylosis, spondylosis deformans, ankylosing spondylosis, Bechterew’s disease, Marie-Strumpell’s disease, Morbus Bechterew-Marie-Strumpell, pelvospondylitis ossificans, rheumatoid ossifying pelvispondylitis, rheumatoid spondylitis, bamboo spine, poker back, spondylitis ankylopoetica, spondylitis deformans, atrophic spondylitis… and others.
Jubb, K. V. F., Kennedy, P. C., and Palmer, N. 1993. Pathology of Domestic Animals. 4th Edition. Volumes 1, 2 and 3. London: Academic Press.
Roberts, C. and Manchester, K. 2005. The Archaeology of Disease. 3rd Edition. Stroud: Alan Sutton Publishing Ltd.
Spencer, D. G., Sturrock, R .D., and Buchanan, W. W. 1980. Ankylosing Spondylitis: Yesterday and Today. Medical History 24: 60-69