Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (13 page)

   Hyperuricemia, related to either increased skin cell turnover or metabolic defect, is found in nearly 20% of patients.

   HLA testing can be helpful: HLA Cw6 is the most important allele for susceptibility to early-onset psoriasis; HLA-B17 may be associated with a more severe phenotype.

Suggested Reading

Cantini F, Niccoli L, Nannini C, et al. Psoriatic arthritis: a systematic review.
Int J Rheum Dis.
2010;13(4):300–317.

REACTIVE ARTHRITIS

   Definition

   Reactive arthritis, formerly known as Reiter syndrome, is an autoimmune spondylarthritis that develops 1–4 weeks after an infection with a pathogen elsewhere in the body. Most often, causing pathogens are urogenital (e.g.,
Chlamydia
) or enteric (e.g.,
Campylobacter
,
Salmonella
,
Shigella
, or
Yersinia
).

   Who Should Be Suspected?

   A likely patient is a young adult (20– 40 years of age) who develops postinfectious asymmetric oligoarthritis (affecting most often the knees, ankles, and heels), enthesitis, dactylitis, and lower back pain. In addition, patients may have extra-articular signs including urinary (urethritis, balanitis, dysuria, prostatitis in men, cervicitis, salpingitis or vulvovaginitis in women), ocular (conjunctivitis or anterior uveitis), and/or constitutional (malaise, fever, weight loss) symptoms.

   Laboratory Findings

Diagnosis is primarily clinical.

   Culture and serology tests are helpful in identifying the infectious etiology of the disease in only a fraction of cases since pathogens may no longer be retrievable by the time arthritis develops. Nevertheless, a trial to identify the following pathogens by stool or urine cultures, or in some cases by serology, should be attempted:

   
Chlamydia
, especially
Chlamydia trachomatis
and
Chlamydia pneumoniae
. PCR for urinary
Chlamydia
DNA has high sensitivity.

   
Yersinia enterocolitica
and
Yersinia pseudotuberculosis
.

   
Salmonella
of various serovars.

   
Shigella
, especially
Shigella flexneri
and
Shigella dysenteriae
.