Last updated: November 5, 2014

Synonyms: Enthesitis, tendonitis (e.g., Achilles tendonitis), plantar fasciitis.

ICD-9 Code: Enthesopathy, unspecified site, 726.90; spinal enthesopathy 720.1.

ICD-10: M76 – M77.9

Definition: A periarticular condition that affects the entheses: entheses are sites where tendons, ligaments, or synovial membrane attach to bone. These may be inflammatory or degenerative or mixed in etiology; rarely they are due to endocrinopathy, trauma, or drugs.

Etiology: In spondyloarthropathy (SpA), a local inflammatory response causes the onset or perpetuation of enthesitis. Factors underlying metabolic or degenerative causes are unknown but may be anatomic or mechanical.

Pathogenesis: There are two types of entheses: fibrous and fibrocartilaginous. The fibrous type is a dense connective tissue that attaches tendon or ligament to membranous bone. The fibrocartilage entheses have a transitional zone of fibrocartilage that attaches to endochondral bone at the epiphyses or apophyses. At these sites, fibrocartilage functions to resist shear and compressive forces. Fibrocartilage entheses are primarily affected in enthesopathy. There are innumerable entheses affected by disease. They often lie adjacent to bursal, synovial, and spinal structures that may also become involved. Inflammation of the entheses is the primary pathology in SpA.

Demographics: Enthesitis is seen in 25% to 60% of patients with SpA; it  may occur at any age or affect either gender. With advancing age, repetitive use or trauma, and factors like obesity, degenerative changes affect the entheses as well.

Disease Associations: Enthesopathy has been reported in a variety of conditions; it is common in SpA (AS, reactive arthritis, psoriatic arthritis, enteropathic arthritis,  juvenile spondylitis, etc.) but also in RA, leprosy, trauma, OA, DISH, acromegaly, fluorosis, retinoid therapy, hypoparathyroidism, hyperparathyroidism, POEMS syndrome, and X-linked hypophosphatemia.

Cardinal Findings: Enthesitis most often manifests as pain;  swelling is more difficult to ascertain. The most common site of involvement is the heel with tenderness at either the distal insertion of the Achilles tendon posteriorly or the proximal insertion of the plantar fascia on the inferior os calcis. Other common sites include the toes and fingers (resulting in sausage digits), above and below the knee, elbow epicondyles, pes anserinus, symphysis pubis, ischium, anterior superior iliac crest, greater trochanter, spinous processes, and costochondral junctions. Enthesitis involving the muscle insertions on the anterolateral ribs may be mistaken for chest pain or pleurisy.

Uncommon Findings: May manifest as low back pain or may be asymptomatic and incidentally found on imaging. Uncommonly enthesitis will result in avulsion or rupture of a tendon.

Diagnostic Tests: Laboratory tests reflect the nature of the underlying pathology and cause. HLA-B27 may be indicated in young patients with an equivocal presentation to suggest a SpA.

Imaging: Radiographs had historically been used to assess enthesial pathologyy. However, plain radiographs largely detect the sequelae of chronic enthesitis, including bony erosions and reactive new bone formation. This may be accompanied by periostitis, periarticular sclerosis, or cysts. Such findings will only be evident with advanced or established disease because such findings take years to be evident. MRI is helpful in the early identification of perientheseal soft tissue edema, thickening of the entheses, early erosion of bone, or adjacent bone marrow edema. MRI is particularly useful in identifying sites of polyenthesopathy. The “shiny corners” or vertebral osteitis associated with SpA are manifest examples of enthesitis on MR imaging. Ultrasonography is effective in delineating enthesopathic abnormalities and improvement with therapy.

Diagnostic Criteria: Enthesitis is one of several criteria included by the European Spondyloarthropathy Study Group for the diagnosis of SpA. Several clinical trials tools have been developed to quantify the degree of enthesitis. These include enthesopathy indices developed by Mander et al. (66 sites), Mastricht et al., the assessment in ankylosing spondylitis (ASAS) enthesitis index (13 regions), and the Leeds Enthesitis Index (LEI; 6 sites).

Differential Diagnosis: Other causes of periarticular pain, including fracture, should be considered (see Nonarticular Disorders).

Therapy: Nonpharmacologic measures (e.g., weight loss, activity modification, stretching, orthotics, splints) may prove useful in some. First-line drug therapy often includes the use of anti-inflammatory doses of NSAIDs, if not otherwise contraindicated.  Although systemic corticosteroids are ineffective and should be discouraged, some patients will benefit from intralesional injections of corticosteroids. Disease-modifying therapy with sulfasalazine or MTX have anecdotally been effective. TNF inhibitor therapy has proven to be highly effective in many cases. There is no role for surgery in most cases.

Kohler L, Kuipers JG, Zeidler HK. Enthesopathy. In: Hochberg MC, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed.Edinburgh: Mosby, 2003:1275–1281.
McGonagle D. Diagnosis and treatment of enthesitis. Rheum Dis Clin North Am 2003;29:549–560. PMID: 12951867

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