The following differential diagnosis was made: sexually transmitted proctitis (most commonly caused by Chlamydia trachomatis, Neisseria gonorrhoeae, herpes simplex virus [HSV], and Treponema pallidum) and inflammatory bowel disease. Acute proctitis in men who have sex with men (MSM) who practice receptive anal intercourse usually represents a sexually transmitted infection (STI). Empiric antibiotic therapy for gonorrhea and chlamydial infection was therefore initiated (ceftriaxone 250 mg intramuscularly as a single dose and doxycycline 200 mg/day for 7 days), while diagnostic study results were pending.

Histology was suggestive of a viral cytopathic effect with positive immunohistochemistry for HPV-p16. Cytology of the anal canal was negative for intraepithelial lesion or malignancy (NILM). Serology was negative for HIV, HAV, HBV, and HCV. Antibody testing for anti-T. pallidum came back negative. However, serology for C. trachomatis (IgM) was equivocal (17 RU/mL).

Positivity for C. trachomatis in molecular biology (polymerase chain reaction) from an anal swab confirmed the diagnosis of infectious proctitis. Results came back negative for gonorrhea and HSV. The patient was advised to notify his sexual partners and explain the need for a medical evaluation. Taking the C. trachomatis positivity into consideration, treatment with doxicillin was extended to 3 weeks and this led to the resolution of symptoms.

Anoscopy after 2 weeks showed no rectal lesions. Ileocolonoscopy performed 3 months later confirmed healing of the rectal lesions. No further lesions were observed. The patient was followed for 12 months and remained asymptomatic.

Infectious proctitis is an increasing diagnosis in MSM [1]. The differential diagnosis between infectious causes (C. trachomatis, gonorrhea, HSV, and syphilis) and noninfectious causes (inflammatory bowel disease and cancer) is difficult in many cases [2, 3].

References

1 Bissessor M, Fairley CK, Read T, Denham I, Bradshaw C, Chen M. The etiology of infectious proctitis in men who have sex with men differs according to HIV status. Sex Transm Dis. 2013 Oct;40(10):768–70.

2 Levy I, Gefen-Halevi S, Nissan I, Keller N, Pilo S, Wieder-Finesod A, et al. Delayed diagnosis of colorectal sexually transmitted diseases due to their resemblance to inflammatory bowel diseases. Int J Infect Dis. 2018 Oct;75:34–8.

3 Santos AL, Coelho R, Silva M, Rios E, Macedo G. Infectious proctitis: a necessary differential diagnosis in ulcerative colitis. Int J Colorectal Dis. 2019 Feb;34(2):359–62.

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