Syphilitic proctitis mimicking ulcerative colitis in a person living with HIV

Abstract

Syphilitic proctitis is a rare presentation of syphilis that can mimic IBD, posing a diagnostic challenge, especially in immunocompromised patients. We report the case of a 28-year-old transgender woman with a past medical history of ulcerative colitis, HIV, and syphilis, initially misdiagnosed with ulcerative colitis. Sigmoidoscopy showed a rectal ulcer; histology and positive syphilis serologies confirmed syphilitic proctitis. This case highlights the need to consider infectious causes in atypical or treatment-resistant proctitis, emphasising the value of a thorough history and targeted testing.

Keywords

Sexual intercourse other syphilis (Treponema pallidum)bacterial disease diagnosis

Introduction

Syphilis is a sexually transmitted disease with numerous clinical manifestations that progress through three stages. Syphilitic proctitis is a very rare manifestation, accounting only for 2% of cases of isolated infectious proctitis after gonorrhea (30%), Chlamydia (19%), and HSV-2 (16%); the remaining 45% of cases are idiopathic in etiology.¹ It can result from anal receptive intercourse and is particularly common among immunocompromised patients living with the human immunodeficiency virus (HIV) as indicated by various case reports.^2–8

Case presentation

A 28-year-old transgender woman living with HIV, with a past medical history of treated latent TB and syphilis, was referred for recurrent rectal bleeding, initially presumed to be an exacerbation of ulcerative colitis (UC). In 2022, she had symptoms of diarrhea and rectal bleeding, and inflammatory bowel disease was suspected. A scheduled colonoscopy later confirmed the diagnosis of UC, and she was started on mesalamine 500 mg QID.

Since 2024, she reported 2–3 formed bowel movements daily with occasional rectal bleeding but with no other GI symptoms. However, 4 months prior to presentation, she developed new-onset painful defecation and worsening rectal bleeding, prompting a flexible sigmoidoscopy in 2025 to evaluate for a possible exacerbation of UC.

The sigmoidoscopy revealed a solitary ulcer in the distal rectum, approximately 2 cm from the anorectal verge, partially circumferential and involving two-thirds of the rectal wall as shown in Figure 1. Biopsy stained with Warthin–Starry silver stain revealed the presence of spirochetes, consistent with Treponema pallidum.

Figure 1.

Sigmoidoscopy Findings. A solitary ulcer was identified in the distal rectum, approximately 2 cm from the anorectal verge, partially circumferential and involving two-thirds of the rectal wall.

The patient reported a prior history of syphilis for which she received appropriate treatment, with subsequent follow-up serologies reportedly non-reactive; however, at the time of current presentation, the RPR was reactive at a titer of 1:4, raising concern for reinfection or reactivation. The patient's CD4 count and viral load were 422 cells/mm³ and <20 copies/mL, respectively. These findings, along with the clinical symptoms, supported a diagnosis of syphilitic proctitis.

Based on the endoscopic and histopathologic findings, along with the persistently reactive RPR serology, a diagnosis of syphilitic proctitis was established. Mesalamine therapy was discontinued, and the patient was initiated on intramuscular benzathine penicillin G. Follow-up care was coordinated with the infectious diseases specialists. The patient reports clinical improvement in symptoms following treatment, and a follow-up endoscopy has not been performed yet to assess for healing.

Discussion

Typical symptoms of syphilitic proctitis include lower abdominal pain, tenesmus, and hematochezia,⁶ all of which are symptoms our patient presented with. Interestingly in a few case reports, the condition presented as a rectal mass that raised concern for malignancy and required a biopsy for diagnosis.^6–8 An asymptomatic presentation has also been reported and was diagnosed incidently after biopsy of a rectal polyp during a routine colonoscopy.⁹ As the aforementioned symptoms are typical of inflammatory bowel disease (IBD) such as UC, a high degree of suspicion is required for a diagnosis of infectious proctitis. A high-risk sexual history, e.g., anal receptive intercourse, points towards infectious proctitis,¹ and a thorough medical history is needed to recognize those cases. Lack of improvement after treatment of suspected IBD, as in our patient, should also raise the suspicion of another etiology.¹

Imaging findings include chancre, ulcers, and mass-like lesions; these findings overlap with other conditions such as malignancy, non-specific inflammatory changes, and inflammatory bowel disease (IBD) and can complicate the diagnosis.^4,6 Upon colonoscopy in our case, a circumferential ulcer was found in the rectum with no mass-like lesions or mucosal friability and other findings suggestive of IBD. This, along with the unresponsiveness to IBD-therapy, raised suspicion towards another diagnosis. A biopsy of the ulcer with the Warthin-Starry stain was positive for spirochetes, which suggests syphilitic proctitis. Syphilis diagnostic studies showed a reactive rapid plasma reagin (RPR) and positive treponemal antibodies, confirming the diagnosis of syphilis.

IBD is the most common cause of proctitis and is thus often the first suspected diagnosis.¹ There is, however, a wide differential for proctitis including infectious causes and non-infectious causes. Symptoms are often similar, and it is difficult to distinguish the cause without a prior degree of suspicion.

Infectious causes are most commonly due to gonorrhea (30%), followed by Chlamydia (19%), HSV-2 (16%), and syphilis (2%); the remaining 45% of cases are idiopathic in etiology.¹ Other infectious causes of proctitis such as Shigella, Campylobacter, Salmonella, Escherichia coli, Entamoeba histolytica, cytomegalovirus, and Clostridium difficileare, are more acute in onset and result in extensive colitis that is not isolated to the rectum.^1,10 Infectious causes are typically more common in immunocomprised individuals and those who participate in anal receptive intercourse,^6,11 as in our case. Immunodeficiency, particularly due to HIV, also raises the risk significantly and should raise the suspicion of an infectious cause. Table 1 summarizes selected case reports with similar characteristics and risk factors to our patient.

Table 1.

Summary of selected syphilitic proctitis case reports.

Reference	Patient demographics	Clinical presentation
Adachi E, et al., 2011²	28-year-old homosexual Japanese man	Diarrhea, painful defecation, hematochezia, abdominal discomfort (1 month)
Arnold CA, et al., 2013³	Nine HIV-positive men who have sex with men (MSM)	Rectal bleeding, pain, tenesmus; endoscopic ulcerations and/or mass lesions
Yang JF, et al., 2016⁴	31-year-old HIV-positive man (CD4 240 cells/mL); history of receptive anal intercourse with multiple homosexual men	Rectal bleeding, tenesmus, 20-pound weight loss, mucoid rectal discharge, blurry vision (11 months); fungating rectal mass; concurrent neurosyphilis
Struyve M, et al., 2018⁵	36-year-old man with family history of Crohn’s disease; history of unprotected anal intercourse	Mushy stools with blood/mucus, perianal discomfort, abdominal pain, fever; elevated C-reactive protein (CRP), highly positive fecal calprotectin; rectal ulcerations

Non-infectious causes are less common than infectious causes and include radiation-associated proctitis, diversion colitis, ischemic colitis, trauma due to foreign bodies, Behcet disease, and lymphoma^1,10; in the case of radiation-induced proctitis, diversion colitis, and ischemic colitis, patients typically have a history of radiation therapy for cancer, ostomy/diversion procedures of the colon, or severe hypotension, respectively.

This case highlights the challenges associated with the diagnosis of syphilitic proctitis and the importance of a thorough medical history and a high degree of suspicion. Early recognition is essential to treat the appropriate cause and prevent potential complications, especially those associated with syphilis, which can be dire and life-threatening in many cases.

Conclusion

This case highlights the importance of maintaining a broad differential when evaluating proctitis, especially in patients with overlapping risk factors such as HIV infection and a history of sexually transmitted infections. Syphilitic proctitis, though rare, can closely mimic inflammatory bowel disease, leading to potential misdiagnosis and inappropriate treatment. A high index of suspicion, detailed sexual and medical history, and appropriate diagnostic testing—including serologic evaluation and tissue biopsy—are essential for accurate diagnosis. Early recognition and targeted antibiotic therapy are crucial to prevent complications and ensure optimal patient outcomes. This case also emphasizes the need for inclusive and individualized language in clinical practice, particularly when describing diverse patient populations.

Footnotes

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Hammam Jallad

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