More Than Meets the Eye

Mimics & More

Dr. Ogdie-Beatty

The final speaker in the session was Alexis Ogdie-Beatty, MD, MSCE, associate professor of medicine, associate professor of epidemiology, Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia. Dr. Ogdie-Beatty explained that, when evaluating for nr-axSpA, a rheumatologist should always be asking, “What else could this be?”

The list of potential mimicking conditions is long and includes mechanical back pain, fibromyalgia, degenerative disc disease, fracture, osteitis condensans ilii, diffuse idiopathic skeletal hyperostosis (DISH), sarcoidosis, crystalline arthritis and septic arthritis.

One key question with which to begin the evaluation is to ask, “Where is the pain?” The specific location of pain, as well as patient age, precipitating factors and relationship to physical activity, will often help inform if this is more or less likely to be mechanical back pain.

Dr. Ogdie-Beatty explained that inflammatory back pain is typically associated with an insidious onset, is worse at night (especially the second half of the night) and improves with activity.

In speaking about other causes of back pain, fibromyalgia is challenging because it can both mimic inflammatory back pain as well as exist as a comorbidity in up to one-third of patients with axSpA.

Osteitis condensans ilii is characterized by benign sclerosis of the ilium adjacent to the SI joints, often appearing bilaterally and with a triangular shape. The condition is more common in women than men, particularly during and after pregnancy. DISH is normally found in men over age 45 and is associated with the presence of diabetes mellitus. It may be asymptomatic and present mostly as decreased range of motion in the spine; enthesophytes are also commonly seen with this condition.

Some other mimics of inflammatory back pain, such as Paget’s disease, X-linked hypophosphatemia and alkaptonuric ochronosis (an autosomal recessive disease that results in buildup of homogentisic acid in cartilage and subsequent arthropathy) are quite rare, but worth at least being aware of.

In Sum

The session was stimulating and highly informative, which comes as a great relief to the rheumatology world that is still trying to better understand the entity of nr-axSpA.

Jason Liebowitz, MD, is an assistant professor of medicine in the Division of Rheumatology at Columbia University Vagelos College of Physicians and Surgeons, New York.

Reference

1. Rudwaleit M, van der Heijde D, Landewé R, et al. The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): Validation and final selection [published correction appears in Ann Rheum Dis. 2019 Jun;78(6):e59]. Ann Rheum Dis. 2009;68(6):777–783.