Differentials
Osteoarthritis
SIGNS / SYMPTOMS
Presents with mechanical pain typically becoming worse at the end of the day and after activity, with no morning symptoms.
May occur after lifting or bending.
The history differentiates mechanical back pain from inflammatory back pain.
INVESTIGATIONS
Radiographs of the back may demonstrate degenerative disk disease or the presence of osteophytes.
Diffuse idiopathic skeletal hyperostosis (DISH)
SIGNS / SYMPTOMS
Typically presents with mechanical symptoms.
Age at onset may help differentiate this condition from AS, as onset tends to be in the 50- to 75-year age group.
INVESTIGATIONS
In DISH there are flowing osteophytes along the anterior margin of the vertebra in the presence of normal vertebral bodies and disks on x-ray.[108]
Psoriatic arthritis
SIGNS / SYMPTOMS
Part of the spondyloarthropathy group.
Tends to present in the 35- to 45-year age group. No sex bias.
Sacroiliitis may be unilateral.
History of psoriasis.
Dactylitis more common.
INVESTIGATIONS
Hand and foot x-rays may reveal erosive disease.
Reactive arthritis
SIGNS / SYMPTOMS
Patients usually recall a specific infection: for example, a nongonococcal urethritis or gastroenteritis.
Dactylitis and skin manifestations occur more frequently than in AS.
May present with keratoderma blennorrhagica, conjunctivitis, or urethral discharge.
INVESTIGATIONS
Pelvic x-rays may demonstrate unilateral sacroiliitis.
Inflammatory bowel-related arthritis
SIGNS / SYMPTOMS
History of Crohn disease or ulcerative colitis.
No sex bias.
Peripheral joint involvement common.
May have evidence of erythema nodosum or pyoderma gangrenosum.
INVESTIGATIONS
Only 30% HLA-B27-positive.
May have unilateral sacroiliitis.
Infection (e.g., discitis)
SIGNS / SYMPTOMS
Patients are usually systemically ill with fever, anorexia, and rigors accompanying back pain.
INVESTIGATIONS
Focal spinal abnormalities on x-ray or MRI.
Elevated inflammatory markers.
Vertebral fracture
SIGNS / SYMPTOMS
May coexist with AS.
Presents as episodic spinal pain.
INVESTIGATIONS
Focal spinal abnormalities on x-ray or MRI.
Bony metastases
SIGNS / SYMPTOMS
Systemic clues such as weight loss, melena, alternating bowel habits, prostate symptoms, breast mass.
INVESTIGATIONS
Radiographs more likely to show vertebral collapse or metastatic deposits.
Ochronotic arthropathy
SIGNS / SYMPTOMS
Rare syndromes, which present in the third and fourth decades with lower back and hip stiffness that can mimic AS.
INVESTIGATIONS
Presence of homogentisic acid in the blood and urine.
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