TABLE 2.
Summary of the Differential Diagnosis of AxSpA
| Chronic Back Pain With Onset in Adolescence or Early Adulthood | Distinguishing Features |
|---|---|
| Degenerative disk disease114–119 | • MBP exacerbated by flexion ± radicular pain radiating below the knee • Risk factors: obesity, genetics, repetitive microtrauma, other injury • Imaging: disk space narrowing. Disk herniation may be visible on MRI |
| Fibromyalgia120–123 | • MBP with widespread pain in other areas of the body, fatigue, and sleep disturbances. Minimal relief with NSAIDs • Risk factors: female sex, obesity, ± adverse childhood experiences • Imaging: no evidence of inflammatory disease or other etiology |
| Spondylolysis and spondylolisthesis124–129 | • MBP exacerbated by hyperextension that may extend into buttocks or posterior thighs • Risk factors: activities with repetitive flexion and extension of the lower back (gymnastics, football, ice skating, weightlifting, etc.) • Imaging: with spondylolysis, separation or fracture of the pars interarticularis (pars defect). With bilateral pars defects, the injured vertebra may be shifted forward relative to the vertebra directly below it (spondylolisthesis) |
| Scheuermann disease130–132 | • MBP occurring in early adolescence without precipitating trauma • Risk factors: male sex, more severe with tall height • Imaging: vertebral wedging (wider posterior vs. anterior angle) and possible Schmorl nodes (protrusion of disk material into the vertebrae) |
| Astrocytomas133,134 | • Gradual or subacute MBP onset, often with subsequent development of sensory or motor dysfunction • Risk factors: genetics, ionizing radiation • Imaging: asymmetrical spinal cord expansion on MRI |
| Mimics of AxSpA on Imaging | Distinguishing Features |
| Osteitis condensans ilii135–138 | • Asymptomatic or nonradicular low back pain that can extend to the posterior thighs • Risk factors: multiparity, other mechanical stress • Imaging: SIJ sclerosis of the iliac side without erosions or fusion |
| DISH139–145 | • Asymptomatic or MBP • Risk factors: male gender, age >50 y, diabetes, obesity • Imaging: flowing bone along the anterolateral vertebral bodies and across the disk space in the thoracic spine with or without lumbar and cervical spine involvement. A lucent area may be seen between the anterior longitudinal ligament and midportion of the vertebral body. SIJs are often unaffected, but the superior aspect of the SIJ may appear fused. Peripheral calcific enthesopathy may occur |
| Infectious sacroiliitis146–151 | • Subacute onset of unilateral buttock or back pain with elevated CRP. Fever is usually absent or low grade • Risk factors: IV drug use, pelvic trauma, infectious endocarditis, immunosuppression, cutaneous or genitourinary infection • Imaging: on MRI, unilateral periarticular muscle edema, thick capsulitis, and extracapsular fluid collection may be useful in differentiating infectious sacroiliitis from sacroiliitis due to axSpA |
| Whipple disease152–161 | • Large joint migratory arthralgias, abdominal pain, weight loss, and diarrhea, with or without IBP • Risk factors: occupational exposure to soil or animals • Imaging: sacroiliitis and spondylitis indistinguishable from axSpA |
| Familial Mediterranean fever143,162–164 | • Intermittent fevers, abdominal pain, large joint arthritis, enthesitis, IBP. Childhood or adolescent onset is typical, but may occur in adulthood • Risk factors: genetics (MEFV gene mutations); Turkish, Armenian, North African, Jewish, and Arab descent • Imaging: sacroiliitis indistinguishable from axSpA |
| Sarcoidosis149,165–170 | • IBP • Risk factors: sacroiliitis may occur most frequently in sarcoidosis limited to the thorax (thoracic lymph nodes and lungs) • Imaging: sacroiliitis indistinguishable from axSpA |
| Spinal calcium pyrophosphate deposition disease171–173 | • Periodic IBP with elevated inflammatory markers • Risk factors: widespread peripheral chondrocalcinosis • Imaging: linear calcium deposition in intervertebral disks, SIJs, and/or peripheral joints |
| Idiopathic hypoparathyroidism174–178 | • Hypocalcemia presentation ± back pain • Risk factors: long-standing hypoparathyroidism • Imaging: syndesmophytes. SIJ usually not involved but subchondral bone resorption or sclerosis may occur |
| Behçet disease179–188 | • Recurrent mucocutaneous ulcers, ocular inflammation, peripheral arthritis, ± entheseal inflammation • Risk factors: HLA-B51 gene; Turkish Japanese, Korean, Chinese, Iranian, Iraqi, Saudi Arabia descent • Imaging: sacroiliitis indistinguishable from axSpA |
| Hereditary hypophosphatemic rickets189–191 | • Growth limitations, osteoarthritis, back pain, enthesopathies • Risk factors: genetics (autosomal recessive) • Imaging: syndesmophytes without inflammatory spinal lesions beginning in the second or third decade of life. SIJs typically spared |
| Ochronosis192–195 | • Hyperpigmentation of skin or sclera, back pain, range-of-motion limitations, and kyphosis beginning in the third decade of life • Risk factors: genetics (autosomal recessive) or exposure to hydroquinone or phenols • Imaging: affects the intervertebral disks and large joints. Ankylosis in the lumbar or thoracic spine may develop later in the disease course. SIJs usually spared |
IV, intravenous; MBP, mechanical back pain.