ANKYLOSING SPONDYLITIS (AS) / MARIE’s Disease / BEKTEREV’s Disease
ANKYLOSING SPONDYLITIS (AS) is a Chronic Autoimmune or Autoinflamatory systemic disease which predominantly affects joints and bones of Spine and Pelvis
It falls under AXIAL SPONDYLOARTHRITIS Category.
CAUSES OF ANKYLOSING SPONDYLITIS
Causes are obscure, though Genetics Environmental Factors and Lifestyle in combination are believed to be involved in causation of Ankylosing Spondylitis (AS)
It falls under Sero-negative Systemic Rheumatic disease where its believed to be mediated by Autoimmune or Autoinflamatory response.
Human Leucocyte Antigen HLA B27 subtypes B2701and B2759 are class I antigen encoded by B locus of Major Histocompatibility Complex (MHC) on Chromosome 6 and presents antigenic peptides (derived from self and non self antigens ) to T cells. HLA B27 is strongly associated with Ankylosing Spondylitis as 90% of patient showing symptoms of Ankylosing Spondylitis has a genotype presenting it. and 2% of all having genotype expressing HLA B27 contracts Ankylosing Spondylosis.
PATHOGENESIS OF ANKYLOSING SPONDYLITIS
Pathogenesis of AS is still not clear and many factors associated with the pathophysiology directly or indirectly have been identified
- Human Leucocyte Antigen (HLA B27 subtypes B2701and B2759) are class I antigen encoded by B locus of Major Histocompatibility Complex (MHC) on Chromosome 6 and presents antigenic peptides (derived from self and non self antigens ) to T cells. HLA B27 is strongly associated with Ankylosing Spondylitis as 90% of patient showing symptoms of Ankylosing Spondylitis has a genotype presenting it. and 2% of all having genotype expressing HLA B27 contracts Ankylosing Spondylosis.Now this association with HLA B27 suggests possible link with CD8 T cells though not proven to involve self antigen it might also be due to reactive arthritis following infection and the antigen might be derived from intracellular microorganism; HLA B27 has many unusual varied properties also it has ability to interact with CD4 so possible association of CD4 in AS is also a probability.
- Tumour Necrosis Factor α (TNF α) is found to b implicated in Ankylosing Spondylitis
- Interleukine 1 (IL 1) is also associated in pathogenesis of Ankylosing Spondylitis
- Anti-Neutrophil Cytoplasmic Antibodies (ANCAs) are associated with Ankylosing Spondylitis but is not indicator of severity of disease
- Autoantibodies Specific to Ankylosing Spondylitis have not been identified
- PTGER4 gene codes for prostaglandin EP4 receptor(EP4). which is associated with bone remodeling and deposition and is highly expressed in those sites of vertebral coloumn which are involved in Ankylosing Spondylitis . Single Neucleotide Polymorphism (SNP) of A/G variant rs10440635a close to the PTGER4 gene on human chromosome 5 possibly influences excessive production of EP4 which causes excessive bone remodelling and deposition in Ankylosing Spondylosis ; though this type of SNP and its association with increased rate of Ankylosing Spondylosis is found only in few ethnic groups
All these and other unknown factors contribute in pathogenesis of Ankylosing Spondylitis which typically results in Annulus Fibrosus Disci Intervertebralis (fibrous ring) of intervertebral disc to OSSIFY which results in the formation of marginal SYNDESMOPHYTES between adjoining vertebrae giving rise to BAMBOO SPINE type appearance of spine
SYMPTOMS AND DIAGNOSIS OF ANKYLOSING SPONDYLITIS
Genetic Testing For Ankylosing Spondylitis
HLA B27 is a non specific test For Ankylosing Spondylitis
As although 90% of those who have AS are HLA B27positive(50% in african-americans and 80% in mediterrenean)
But it has seen in many ethnic group ;esp north scandivanian;that Only 2 % of total HLA B27 positive have AS
Blood Test for Ankylosing Spondylitis
There are no specific Blood Tests Available for AS except for general inflamatory indicators like ESR and CRP which are elevated and tend to increase further on acute episode
Radiological Investigation For Ankylosing Spondylitis
There are no specific Blood Tests Available for AS So its diagnosed based on typical radiological changes but it takes 8-10 years for the disease to become evident enough to establish diagnosis neither CT or MRI can evaluate the disease in early stages
Typical radiological features are:-
- Axial Spondyloarthritis
- Early Xray changes include erosion and sclerosis of sacroilliac joints
- in later stage that erosion increases resulting in pseudo-widening of joint space and Bony Ankylosis
- squaring of vertebrae with spine ossification with fibrous band running longitudinally called syndesmophyte giving a bamboo spine appearance
Now in case where there are no evident radiological signs it becomes difficult to establish diagnosis as there are no specific blood tests for AS. In such cases clinical features signs symptoms and other non specific blood tests are conducted to evaluate the probability of AS; they are :
- Chronic backache with insidious onset before age of 40yrs which has peculiar modalities- Aggravates on rest ;at night and Ameliorates on moderate movement ;exercise ; after getting up from bed in morning
- History of inflamatory arthritis or tendinitis
- Family history of axial Spondylosis
- Positive HLA B27
- Responds well to NSAIDs
- Elevated ESR and CRP
- Other accompaning conditions like IBS Uveitis psoriasis
- Schober’s test is a clinical performed during physical exam which is measure of flexion of lumbar spine.
BATH ANKYLOSING SPONDYLITIS DISEASE ACTIVITY INDEX
BASDAI index score is an index which is based on multiple clinical radiological genetic and blood parameters which helps in establishing stage and diagnosis and determine type of management and treatment required
BATH ANKYLOSING SPONDYLITIS FUNCTIONAL INDEX
BASFI index to acess functional impairment
HUNCHED POSTURE is a severe complication of AS resulting due to complete spinal fusion leading to increased spinal KYPHOSIS which results into forwar and downward shift of Center of Mass to compensate it the knee flexes and ankle dorsiflexes.Their gait has a cautious pattern as they have reduced shock absorbing ability and cant see horizon.