Microbiology · Year 2 · from Microbiology
Case 3: Chlamydial Urethritis and Reactive Arthritis
Presentation
A 25-year-old man presents with dysuria and urethral discharge for 1 week. He also reports pain and swelling in his left knee and right heel for the past 3 days, along with eye redness. He had unprotected intercourse with a new partner 3 weeks ago. Examination reveals mucopurulent urethral discharge, a swollen left knee with effusion, Achilles tendinitis on the right, and bilateral conjunctival injection. Gram stain of urethral discharge shows numerous neutrophils but no organisms.
Clinical Image
Clinical findings in reactive arthritis triggered by Chlamydia trachomatis: mucopurulent urethral discharge (urethritis) and conjunctival injection (conjunctivitis), along with arthritis - formerly called Reiter syndrome.
Image Source: Lecture image - Chlamydia trachomatis clinical syndromes
Questions
- What is the likely diagnosis, and what organism is most likely responsible for the triggering infection?
- Why does the Gram stain show neutrophils but no organisms?
- What is the pathophysiology of the joint and eye manifestations?
- What is the appropriate management of this patient?
Answers
- Diagnosis and triggering organism: This patient has reactive arthritis (formerly Reiter syndrome) triggered by Chlamydia trachomatis urethritis. The classic triad is: "can't see, can't pee, can't climb a tree" - conjunctivitis, urethritis, and arthritis. The antecedent genitourinary infection with mucopurulent discharge (non-gonococcal urethritis) and the temporal relationship with joint symptoms support this diagnosis. Reactive arthritis can also follow enteric infections (Salmonella, Shigella, Campylobacter, Yersinia).
- Gram stain findings: Chlamydia trachomatis cannot be visualized on Gram stain for several reasons: the organisms are too small (0.2-0.4 μm), they are obligate intracellular pathogens and thus not present extracellularly in discharge, and they have minimal peptidoglycan and do not retain Gram stain. The finding of neutrophils without visible organisms is characteristic of non-gonococcal urethritis (NGU) and should prompt testing for Chlamydia (and Mycoplasma genitalium).
- Pathophysiology of extragenital manifestations: Reactive arthritis is an immune-mediated inflammatory response to infection, not direct infection of the joints or eyes. There is a strong association with HLA-B27 antigen. The mechanism likely involves:
- Molecular mimicry between bacterial antigens and host tissues
- Chlamydial persistence in joint tissue (controversial)
- Dysregulated immune response in genetically susceptible individuals
The arthritis is typically asymmetric, oligoarticular, and preferentially affects lower extremities. Enthesitis (inflammation where tendons insert into bone, such as Achilles) is characteristic.
- Management:
- Treat the Chlamydia infection: Azithromycin 1g single dose or doxycycline 100 mg twice daily for 7 days
- Partner treatment is essential to prevent reinfection
- Symptomatic treatment of arthritis: NSAIDs are first-line
- Severe or persistent cases may require DMARDs (sulfasalazine) or TNF inhibitors
- Conjunctivitis is usually self-limited; if severe, ophthalmology evaluation
- Test for other STIs including HIV
- Most cases resolve within 6-12 months, but chronic or recurrent arthritis occurs in approximately 15-30% of patients