Foot rash and joint pain

Dx: Keratoderma blenorrhagicum

The patient’s history, clinical findings, and lab results, including a positive Chlamydia trachomatis polymerase chain reaction (PCR) test from a urethral swab, pointed to a diagnosis of keratoderma blenorrhagicum in association with reactive arthritis (following infection with C trachomatis).

Reactive arthritis features a triad of conjunctivitis, urethritis, and arthritis that follows either gastrointestinal or urogenital infection.

Relevant diagnostic findings included an elevated CRP of 26.5 mg/L (normal range, < 10 mg/L), an elevated ESR of 116 mm/h (normal range, < 15 mm/h) and as noted, a positive C trachomatis PCR test. The patient’s white blood cell count was 9.7/μL (normal range, 4.5-11 μL) and the rest of the CBC was within normal limits. Urinalysis was positive for leukocytes and rare bacteria. A treponemal antibody test was negative.

Additionally, the punch biopsy from the right elbow revealed acanthosis, intercellular spongiosis, and subcorneal pustules consistent with localized pustular psoriasis or keratoderma blenorrhagicum. After the diagnosis was made, human leukocyte antigen B27 allele (HLA-B27) testing was conducted and was positive.

A predisposition exacerbates the infection

Reactive arthritis, a type of spondyloarthropathy, features a triad of conjunctivitis, urethritis, and arthritis that follows either gastrointestinal or urogenital infection.¹ Reactive arthritis occurs with a male predominance of 3:1, and the worldwide prevalence is 1 in 3000.¹ Causative bacteria include C trachomatis, Yersinia, Salmonella, ­Shigella, and Campylobacter, Escherichia coli, Clostridioides (formerly Clostridium) difficile, and C pneumoniae.² Patients with the HLA-B27 allele are 50 times more likely to develop reactive arthritis following infection with the aforementioned bacteria.¹

Findings consistent with a diagnosis of reactive arthritis include a recent history of gastrointestinal or urogenital illness, joint pain, conjunctivitis, oral lesions, cutaneous changes, and genital lesions.³ Diagnostic tests should include arthrocentesis with cultures or PCR and cell count, ESR, CRP, CBC, and urinalysis. HLA-B27 can be used to support the diagnosis but is not routinely recommended.²

Pustules and psoriasiform scaling characterize this diagnosis

The differential diagnosis for the signs and symptoms seen in this patient include disseminated gonococcal arthritis, psoriatic arthritis, rheumatoid arthritis, and secondary syphilis.

Gonococcal arthritis manifests with painful, sterile joints as well as pustules on the palms and soles, but not with the psoriasiform scaling and desquamation that was seen in this case. A culture or PCR from urethral discharge or pustules on the palms and soles could be used to confirm this diagnosis.³

Continue to: Psoriasis in association with psoriatic arthritis