Seronegative spondyloarthropathies

Introduction

Among the thousands of patients whom you might want to diagnose with mechanical low back pain, one or two might actually have one of the seronegative spondyloarthropathies, an important group of systemic diseases, which requires careful and particular management.

The seronegative spondyloarthropathies are:

• Seronegative (= negative for rheumatoid factor and anti-citrullinated protein antibodies)
• Spondyloarthropathies ( = predilection for the axial spine and sacroiliac joints)
• Human leukocyte antigen (HLA)-B27 associated
• Associated with asymmetric, large joint polyarthritis
• Associated with extra-articular manifestation (e.g., anterior uveitis, enthesitis)

The Back Pain

With regard to back pain, the history that these patients provide won’t fit the usual mechanical back pain script. These patients will complain of stiffness more than pain, particular in the morning. They won’t have an inciting event, they are not necessarily obese or sedentary, and their pain is not radicular in nature. In addition, the review of systems will sometimes be positive for arthritis, eye problems, diarrhea, and other systemic manifestation.

The Four Seronegative Spondyloarthropathies

1. Ankylosing spondylitis: this usually presents with an insidious onset of morning stiffness and pain in a younger (<40), often male, patient. The pain and stiffness improves with activity. Ankylosing spondylitis is often associated with uveitis (erythema, pain, blurry vision, photophobia, lacrimation), enthesitis (inflammation at the site of tendon or ligament insertion into bone), peripheral joint involvement, kyphosis, restrictive lung disease, and cardiovascular problems. To start the workup, get a CBC, ESR and an AP radiograph of sacroiliac joints (looking for a “bamboo spine” and loss of definition along the margins of the sacroiliac joints). In patients with a high pretest probability for ankylosing spondylitis, a negative plain radiograph should prompt consideration of an MRI of the sacroiliac joints, which is the most sensitive imaging study. Patients with ocular complaints should be referred to an ophthalmologist promptly.
2. Reactive arthritis: this usually presents in a younger patient with (a) asymmetric sterile arthritis, (b) urethritis, and (c) conjunctivitis, in the setting of recent dysuria or diarrheal illness. Keratoderma blenorrhagicum is a rare rash that is very specific for reactive arthritis. Get plain radiographs of involved joints, urinalysis, genital swab or PCR of urine for Chlamydia and/or work up any diarrhea for infectious causes.
3. Psoriatic arthritis: look for  a distal polyarthritis involving the distal interphalangeal joints, and well-circumscribed, erythematous, scaly plaques on extensor surfaces. Also seen is dactylitis (defuse fusiform swelling of an entire digit), and nail changes (nail pitting, onycholysis). Resorption of the distal middle phalanges with telescoping into the distal phalanges leads to the  charecteristic pencil-in-cup deformity on hand radiographs. Explosive eruptions of widespread psoriatic lesions in a previously asymptomatic individuals should make one consider HIV infection.
4. Enteropathic arthritis: associated with inflammatory bowel disease or Whipple’s disease. Send these patients for endoscopy.