Evaluation of anorectal symptoms in men who have sex with men

INTRODUCTION — Anorectal symptoms in men who have sex with men (MSM) may be caused by conditions related to infections for which they are at increased risk (eg, proctitis, perianal abscess/anal fistula, anal warts/dysplasia, human papillomavirus-associated anal cancer) or conditions seen in the general population (eg, anal fissure, hemorrhoids, pruritus ani) [1-5].

The evaluation of anorectal symptoms in MSM will be addressed in this topic. The management of common anal problems in the general patient population, with the exception of proctitis, which is covered here, are discussed separately. (See "Perianal and perirectal abscess", section on 'Management' and "Anorectal fistula: Clinical manifestations and diagnosis" and "Condylomata acuminata (anogenital warts): Management of external condylomata acuminata in adult males" and "Clinical features and staging of anal cancer" and "Anal fissure: Medical management" and "Anal fissure: Surgical management" and "Home and office treatment of symptomatic hemorrhoids" and "Surgical treatment of hemorrhoidal disease" and "Approach to the patient with anal pruritus", section on 'Management'.)

ANATOMY — The anal canal, which is surrounded by internal (involuntary) and external (voluntary) sphincter muscles, extends 2.5 to 3.5 cm to the anal verge (visible lower edge of sphincter) inferiorly. In the mid-point of the anal canal is the dentate line, which is the demarcation between columnar epithelium superiorly and squamous epithelium inferiorly (figure 1). Along the dentate line lie crypts, which have small glands at their base. The squamous epithelium between the dentate line and anal verge is called “anoderm,” which is similar to normal skin but highly sensitive, and the squamous epithelium outside the anal verge is the perianal skin.

DIAGNOSTIC EVALUATION

General approach — The cause of anorectal symptoms in men who have sex with men (MSM) is often suggested by history and physical examination findings (table 1). Patients should be evaluated by obtaining a detailed history, performing an external rectal exam for visible abnormalities (eg, anal warts, hemorrhoids) and performing a digital rectal exam for palpable abnormalities (eg, perianal abscess, rectal mass). In addition, anoscopy is recommended for patients with rectal pain, bleeding, and/or bloody or purulent discharge and in patients with a palpable abnormality on digital rectal exam. (See 'History' below and 'Physical examination' below and 'Anoscopy' below.)

If digital rectal exam reveals a palpable abnormality that cannot be visualized on anoscopy, flexible sigmoidoscopy may be used initially to evaluate the cause of anorectal lesions. Depending upon the finding, such as a mass lesion or other lesion suspicious for neoplasia, the patient should be referred for transrectal ultrasound or pelvic magnetic resonance imaging (MRI) scan (with and without contrast) to determine if the finding represents a cystic or solid lesion. The former would be suggestive of a perianal abscess, while the latter would raise concern for anal cancer.

Tests for gonorrhea, chlamydial infection, herpes simplex virus (HSV) infection, and syphilis, should be obtained in all patients and an anal Pap test should be obtained in those who have not had it performed within the past 12 months. We check these studies, even if the clinical presentation is not suggestive of proctitis or human papillomavirus (HPV)-related disease, given the high risk of these pathogens in MSM. (See 'Laboratory studies' below and 'Anal Pap test' below.)

If the patient has unexplained hematochezia following the initial evaluation, sigmoidoscopy or colonoscopy is recommended; colonoscopy is recommended in patients ≥45 years old, in whom the risk of premalignant polyps and colon cancer is greater. (See "Approach to minimal bright red blood per rectum in adults".)

History — History should include a description of current symptoms, prior anorectal issues, and predisposing behaviors or medical conditions.

Rectal pain and bleeding are common symptoms with various anorectal conditions (table 1). Other historical features might help to narrow the potential causes. Purulent discharge with a history of receptive anal intercourse or prior sexually transmitted infections (STIs) is suggestive of proctitis [1,6]. Purulent discharge can also be a manifestation of a draining perianal abscess, which may be associated with fever or chills, or an anal fistula. Rectal bleeding and pain that occur with defecation are characteristic of anal fissure or hemorrhoids. Patients with anal fissure may have a history of receptive anal intercourse, chronic constipation, or prior anal fissures. The presence of weight loss may indicate anal cancer, particularly if there is a prior history of anal warts or dysplasia [7-9]. Perianal itchiness is suggestive of pruritus ani. There may be similar prior episodes reported.

If the patient has diarrhea as a prominent symptom, proctocolitis or enteritis should be considered as possible etiologies. (See 'Clinical manifestations and diagnosis' below.)

Physical examination — Physical examination should include careful inspection of the skin and mucous membranes, as well as palpation of the inguinal lymph nodes for enlargement or tenderness. Visual inspection of the anus should precede digital exam. The external rectal exam may be normal in patients with proctitis, perianal abscess/anal fistula, anal cancer, and anal fissure, but drainage may be visible in some patients with proctitis or perianal abscess/anal fistula (table 1). Skin-colored papular lesions may be seen externally in patients with anal warts, and dilated veins may be identified in patients with hemorrhoids. Inflamed skin is present in patients with pruritus ani.

Digital rectal exam should be performed using 5% lidocaine ointment if pain is the presenting symptom. The lubricated pad of the examiner digit should be slowly introduced through the anus, and the finger should be inserted fully into the rectum with circumferential palpation for any abnormalities. Digital rectal exam will generally be normal in patients with anal warts/dysplasia and pruritus ani. It often shows tenderness in patients with proctitis, perianal abscess/anal fistula, anal fissure, and hemorrhoids. As noted above, severe pain on examination suggests ulceration in the anal canal. Submucosal fullness is present in patients with perianal abscess/anal fistula and rectal cancer.

Laboratory studies — Because MSM are at increased risk for infectious proctitis and anogenital STIs, we advise STI testing in all such patients with anorectal symptoms. STI tests should include:

●Anal swab for gonorrhea (nucleic acid amplification test [NAAT] or culture)

●Anal swab for chlamydia (NAAT)

●Swab of rectal lesion for HSV (polymerase chain reaction [PCR]), if applicable

●Blood serology and darkfield microscopy of lesion (if applicable) for syphilis

●Anal Pap test, if it has not been performed within the past 12 months [10] (see 'Anal Pap test' below and "Anal squamous intraepithelial lesions: Epidemiology, clinical presentation, diagnosis, screening, prevention, and treatment", section on 'Screening for anal SIL')

If the Chlamydia trachomatis test is positive on a rectal swab, a PCR test for lymphogranuloma venereum should be performed for confirmation of the diagnosis, if available. (See "Lymphogranuloma venereum", section on 'Diagnosis'.)

All MSM with proctitis should be screened for other STIs (eg, human immunodeficiency virus [HIV] infection, hepatitis C virus infection) as well. (See "Screening for sexually transmitted infections" and "Screening and diagnosis of chronic hepatitis C virus infection".)

Anal Pap test — Because MSM are at increased risk for HPV-related disorders (eg, anal warts/dysplasia, anal cancer), we advise anal Pap testing in all MSM with anorectal symptoms who have not had it performed within the past 12 months. Data are limited to support general screening recommendations for anal Pap testing in MSM or other populations [10]. (See "Anal squamous intraepithelial lesions: Epidemiology, clinical presentation, diagnosis, screening, prevention, and treatment", section on 'Screening for anal SIL'.)

The technique consists of inserting a Dacron swab 2 to 4 cm into the anal canal and rotating it 360 degrees while it is removed very slowly. It is fixed in the same manner and interpreted using identical criteria as a cervical Pap smear (atypical squamous cells of undetermined significance [ASCUS], low-grade squamous intraepithelial lesion [SIL], high-grade SIL).

Standardized approaches for the management of anal dysplasia have been developed. If abnormal anal cytology is present, high-resolution anoscopy is recommended. It is performed in a similar manner to colposcopy, utilizing a microscope to better visualize the anal canal, in order to identify abnormal areas and obtain biopsy samples. The tissue is evaluated with both acetic acid (abnormal tissue appears white) and Lugol’s iodine (abnormal tissue does not stain). Histopathology of these biopsy sites allows for grading to determine the severity of disease and further management. Such techniques though may not be widely available. Although abnormal anal cytology is highly predictive of anal dysplasia [11], there are no outcome studies documenting a reduction in mortality. (See "Anal squamous intraepithelial lesions: Epidemiology, clinical presentation, diagnosis, screening, prevention, and treatment".)

Anoscopy — Anoscopy is recommended for patients with rectal pain, bleeding, and/or bloody or purulent discharge and in patients with a palpable abnormality on digital rectal exam. It is performed using a small, rigid, tubular instrument called an anoscope. Lubricant is applied, and the instrument is inserted into the anus, after which the obturator (central conical structure) is removed. Each quadrant of the anal canal is examined with the aid of a bright light as the instrument is slowly removed. Lesions of the anal canal, including internal hemorrhoids, fissures, mucosal abnormalities (eg, warts, proctitis), abscesses, and tumors, can be visualized and biopsied as indicated.

Imaging — Radiologic imaging is usually not necessary for the evaluation of anorectal symptoms but is warranted in patients clinically suspected of having either a perianal abscess or anal cancer (see 'General approach' above and 'Perianal abscess/anal fistula' below and 'Anal cancer' below). Transrectal ultrasound or pelvic MRI scan (with and without contrast) is preferred in this setting.

When to refer — Referral to a gastroenterologist or a rectal surgeon for further evaluation and management is recommended in the following situations:

●Proctitis that does not response to antibiotic therapy or is of unclear etiology

●Perianal abscess/anal fistula

●Suspected anal cancer

●Anal fissure or hemorrhoids that do not respond to conservative management

●Unexplained hematochezia

ETIOLOGIES — Causes of anorectal symptoms in men who have sex with men (MSM) range from conditions that result from receptive anal intercourse or other sexual behaviors to common conditions seen in the general population. MSM have increased rates of sexually transmitted infections (STIs) compared with matched controls [12]. These STIs include HIV infection, gonorrhea, chlamydial infection, herpes simplex virus (HSV) infection, syphilis, and human papillomavirus (HPV) infection. Anogenital HPV infection is associated with a range of clinical manifestations, including anal warts, dysplasia, and cancer [13-15].

Anorectal conditions have characteristic clinical features, and many can be diagnosed on physical examination (table 1) [16]. (See 'Diagnostic evaluation' above.)

Proctitis — Acute proctitis, which is inflammation of the rectum, can be infectious in origin or, less commonly, a manifestation of inflammatory bowel disease (see "Clinical manifestations, diagnosis, and prognosis of ulcerative colitis in adults"). In MSM, it is most often reported in persons who practice receptive anal intercourse. Infectious causes include gonorrhea, chlamydial infection, HSV infection, syphilis, and mpox (previously referred to as monkeypox) [10]. Gonorrheal rectal infection frequently results in proctitis, whereas chlamydial infection is sometimes asymptomatic [17]. However, outbreaks of proctitis related to lymphogranuloma venereum (LGV), which is caused by Chlamydia trachomatis serovars L1, L2, and L3, have been reported in MSM [18-20]. LGV proctitis causes ulcers, which present with hematochezia and rectal pain. (See "Lymphogranuloma venereum".)

Clinical manifestations and diagnosis — Infectious proctitis presents with the acute onset of rectal pain, bleeding, and/or purulent discharge often associated with urgency. External rectal exam is usually normal but may show discharge, and digital rectal exam is noteworthy for diffuse tenderness.

The diagnosis of acute proctitis is suspected from history and physical examination, and the etiology is usually established with STI testing.

Proctitis should be distinguished from proctocolitis and enteritis, which both present with abdominal cramping and diarrhea (for proctocolitis, these symptoms occur in association with symptoms of proctitis). Enteric pathogens causing proctocolitis, such as Campylobacter, Shigella, Salmonella, Giardia, and Entamoeba histolytica, are not generally considered to be STIs, but sexual transmission is well described among MSM [21]. These conditions are discussed elsewhere. (See "Causes of acute infectious diarrhea and other foodborne illnesses in resource-abundant settings" and "Approach to the adult with acute diarrhea in resource-abundant settings".)

In men with proctitis, anoscopy may show evidence of mucosal inflammation or friability. The presence of ulcerations may suggest LGV, HSV infection, or syphilis as the cause. A Gram stain should be performed on any discharge to confirm the presence of polymorphonuclear leukocytes. A detailed outline of recommended diagnostic tests is discussed above. (See 'Laboratory studies' above.)

In May 2022, cases of mpox presenting with lesions confined to the genital or perianal area have been reported [22-24]. Evaluation and diagnosis of mpox proctitis is discussed elsewhere. (See "Epidemiology, clinical manifestations, and diagnosis of mpox (monkeypox)", section on 'Proctitis/tonsillitis' and "Epidemiology, clinical manifestations, and diagnosis of mpox (monkeypox)", section on 'Diagnostic testing'.)

All MSM with proctitis should be screened for other STIs (eg, HIV infection, hepatitis C virus infection). (See "Screening for sexually transmitted infections" and "Screening and diagnosis of chronic hepatitis C virus infection".)

Management — Acute proctitis in MSM who practice receptive anal intercourse usually represents an STI [25]. Empiric antibiotic therapy should be given to patients with rectal discharge pending diagnostic study results (algorithm 1).

●For all patients with proctitis, we suggest treatment for gonorrhea and chlamydial infection. Ceftriaxone intramuscularly as a single dose (500 mg for individuals <150 kg or 1 g for individuals ≥150 kg) and doxycycline (100 mg orally twice a day) for seven days is the typical regimen. (See "Treatment of uncomplicated gonorrhea (Neisseria gonorrhoeae infection) in adults and adolescents", section on 'Preferred regimen' and "Treatment of Chlamydia trachomatis infection", section on 'Antibiotic regimens in adults and adolescents'.)

●For patients who present with perianal or mucosal ulcers, we suggest treatment for HSV infection as well. Valacyclovir 1 gram orally twice a day for 7 to 10 days, famciclovir 500 mg orally twice a day for 7 to 10 days, or acyclovir 400 mg orally three times a day for 7 to 10 days are typical regimens. Longer courses may be necessary in patients who do not have resolution of symptoms at the conclusion of treatment and in patients with HIV. (See "Treatment of genital herpes simplex virus infection".)

●For patients who present with perianal or mucosal ulcers and/or a bloody rectal discharge, we suggest treating for LGV if they have HIV or a positive rectal chlamydia NAAT. This entails extending the doxycycline course to three weeks. (See "Lymphogranuloma venereum", section on 'Treatment of LGV'.)

All patients with a positive diagnostic study for HSV infection (PCR or culture) or syphilis should be treated for the appropriate infection. (See "Treatment of genital herpes simplex virus infection" and "Syphilis: Treatment and monitoring".)

These recommendation are in accordance with guidelines from the Centers for Disease Control and Prevention (CDC) [10,26]. Other published guidelines advocate awaiting microbiologic results before initiating therapy in patients with mild symptoms and empiric coverage for HSV infection and syphilis, as well as gonorrhea and chlamydial infection, in patients with severe symptoms [27]. Studies defining the optimal antimicrobial regiments for acute proctitis are limited, and the selection of drugs is based on treatment evidence for other types of infections with these pathogens.

Appropriate clinical follow-up should be arranged to confirm resolution of symptoms. For proctitis associated with gonorrhea or chlamydial infection, testing for reinfection with the respective pathogen should be performed three months after treatment. Recent partners of patients with infectious proctitis should be evaluated, tested, and presumptively treated for the respective pathogen. Failure to respond should prompt reassessment including repeat cultures and perhaps flexible sigmoidoscopy with biopsy. (See "Treatment of Chlamydia trachomatis infection", section on 'Proctitis and rectal infection'.)

Perianal abscess/anal fistula — Perianal abscess (picture 1) and anal fistula originate from an infected anal crypt gland and represent different manifestations of the same disease process. Perianal abscess presents with pain, bleeding, and/or discharge, especially with defecation, and may be recurrent. Localized or diffuse tenderness and submucosal fullness are present on digital rectal exam. Anal fistula presents as a “non-healing” perianal abscess or with chronic purulent discharge. Discharge or a fistula tract may be visible in the perianal area. The diagnosis of perianal abscess is suggested by physical examination and confirmed by transrectal ultrasound or pelvic magnetic resonance imaging (MRI) scan (with and without contrast) showing a cystic lesion followed by incision and culture of its contents. Surgery may be required for perianal abscess (incision and discharge) and anal fistula (fistulotomy). Details of management are described elsewhere. (See "Perianal and perirectal abscess", section on 'Management' and "Anorectal fistula: Clinical manifestations and diagnosis", section on 'Management'.)

Anal warts/dysplasia — Anal warts (picture 2) and dysplasia are generally asymptomatic. There may be a history of previous anogenital HPV-related conditions (eg, warts, dysplasia). Anal warts, which vary considerably in number and size, appear as skin-colored papular lesions that may be visible on external rectal exam. Digital rectal exam is usually normal, and anoscopy may show white papular mucosal lesions, which represent internal warts. The diagnosis of anal warts is established by physical examination, and the diagnosis of anal dysplasia by Pap test. Anal Pap test technique is described below. (See 'Anal Pap test' above.)

Management of anal warts consists of either a patient-applied (eg, imiquimod, podophyllotoxin) or clinician-administered (eg, cryotherapy, trichloroacetic acid) therapy (see "Condylomata acuminata (anogenital warts): Management of external condylomata acuminata in adult males"). Management of anal dysplasia is described elsewhere. (See "Anal squamous intraepithelial lesions: Epidemiology, clinical presentation, diagnosis, screening, prevention, and treatment".)

Anal cancer — Anal cancer is more common in MSM than in the general population [15], and the risk increases dramatically among those who have HIV. In a population-based survey that examined cancer rates among acquired immunodeficiency syndrome (AIDS) patients from 1980 to 2006, the incidence of AIDS-related cancers (eg, Kaposi sarcoma) declined sharply, while the incidence of some non-AIDS-defining cancers (eg, anal cancer), increased [28]. Among patients with anal cancer, those with HIV infection were younger at the time of diagnosis than those without HIV infection [28].

Anal cancer, which is generally of the squamous cell type, presents with rectal bleeding and/or tenesmus. The stool caliber may be reduced in size, and there may be a recent history of weight loss. There may be a history of previous HPV-related conditions (eg, warts, dysplasia). External rectal exam is generally normal, and a nontender firm mass is often detectable on digital rectal exam. The diagnosis of anal cancer is suggested by physical examination and confirmed by transrectal ultrasound or pelvic MRI scan (with and without contrast) followed by biopsy. Management, which consists of chemoradiation, is described elsewhere. (See "Clinical features and staging of anal cancer", section on 'Clinical features' and "Treatment of anal cancer", section on 'Squamous cell cancer of the anal canal'.)

Anal fissure — Anal fissure is a longitudinal tear in the lining of the anal canal distal to the dentate line (picture 3). A fissure can be primary (eg, resulting from local trauma) or, less commonly, secondary to an underlying medical condition (eg, malignancy, infection, Crohn disease). Anal fissure, which may be recurrent, presents with intense pain, which is especially noticeable with defecation, and intermittent bleeding. The blood is bright red and may drip into the toilet with defecation or be noted on the toilet paper. The fissure is often located on the posterior anal midline and may be seen on anoscopy. They occur more frequently in MSM who engage in receptive anal intercourse and are also associated with chronic constipation. The diagnosis of anal fissure is established by physical examination.

Initial management consists of conservative measures (eg, increased dietary fiber, use of a stool softener, sitz baths) in combination with a topical vasodilator (eg, nifedipine 0.3% ointment applied three times per day) to relax the anal sphincter muscle. Patients should be instructed to refrain from receptive anal intercourse during the healing phase. Fissures refractory to medical management may require surgical intervention. (See "Anal fissure: Medical management" and "Anal fissure: Surgical management".)

Hemorrhoids — Hemorrhoids (picture 4 and picture 5) are normal vascular structures in the anal canal, arising from a channel of arteriovenous connective tissues that drains into the superior and inferior hemorrhoidal veins. They are located in the submucosal layer in the lower rectum and may be external, internal, or mixed based upon their location with respect to the dentate line. Internal hemorrhoids are graded according to the degree to which they prolapse from the anal canal.

Symptomatic hemorrhoids, which are frequently recurrent, most often present with bleeding, especially with defecation. The blood is bright red and may drip into the toilet with defecation or be noted on the toilet paper. Thrombosed external hemorrhoids are characterized by pain and tenderness. Hemorrhoids, which appear as dilated blood vessels, may be visible on external rectal exam. Digital rectal exam may reveal tenderness, and internal hemorrhoids may be seen on anoscopy. The diagnosis of hemorrhoids is established by physical examination. (See "Hemorrhoids: Clinical manifestations and diagnosis".)

Initial management of hemorrhoids consists of conservative measures (eg, increased dietary fiber, use of a stool softener, sitz baths); topical analgesic or antiinflammatory creams may be helpful in some cases. For patients who do not respond to conservative management, office-based procedures, including rubber band ligation, sclerotherapy, and infrared coagulation, may be warranted. Larger hemorrhoids and those associated with rectal prolapse may require surgical excision. Acutely thrombosed external hemorrhoids, which usually respond to conservative measures, can be managed with office-based excision if pain control is problematic. (See "Home and office treatment of symptomatic hemorrhoids" and "Surgical treatment of hemorrhoidal disease".)

Pruritus ani — Anal pruritus (picture 6) is usually idiopathic and thought related from accumulation of moisture, rubbing of the buttocks together with walking, and inadequate hygiene. Wiping the area with toilet paper and scratching perpetuate the symptom. In a minority of cases, anal pruritus may be caused by other conditions, including pinworm, fungal infection of the skin, or noninfectious dermatitis (eg, psoriasis). External rectal exam shows inflamed anal skin. For the patient with suspected pinworm, a tape test for Enterobius vermicularis eggs can be performed. Management of anal pruritus consists of addressing any underlying cause(s) and conservative measures (eg, improving anal hygiene, use of zinc oxide ointment to protect anal skin, and topical hydrocortisone and an oral antihistamine as needed to manage itch). Topical capsaicin may be effective for management of refractory cases. (See "Approach to the patient with anal pruritus", section on 'Management'.)

SUMMARY AND RECOMMENDATIONS

●General approach

•Anorectal symptoms in men who have sex with men (MSM) may be caused by conditions related to infections for which they are at increased risk (eg, proctitis, perianal abscess/anal fistula, anal warts/dysplasia, anal cancer) or conditions seen in the general population (eg, anal fissure, hemorrhoids, pruritus ani) (table 1). (See 'Introduction' above.)

•The cause of anorectal symptoms in MSM is often suggested by history and physical examination findings (table 1). Patients should be evaluated by obtaining a detailed history, performing an external rectal exam for visible abnormalities, and performing a digital rectal exam for palpable abnormalities. In addition, anoscopy is recommended for patients with rectal pain, bleeding, and/or bloody or purulent discharge and in patients with a palpable abnormality on digital rectal exam. If digital rectal exam reveals a palpable abnormality that cannot be visualized on anoscopy, the patient should be referred for transrectal ultrasound or pelvic magnetic resonance imaging (MRI) scan (with and without contrast) to determine if the finding represents a cystic or solid lesion. (See 'General approach' above.)

●Proctitis − Infectious proctitis presents with the acute onset of rectal pain, bleeding, and/or purulent discharge. External rectal exam is usually normal but may show discharge, and digital rectal exam is noteworthy for diffuse tenderness. Sexually transmitted infection tests should include anal swabs for gonorrhea (nucleic acid amplification test [NAAT] or culture), chlamydia (NAAT), herpes simplex virus (HSV; polymerase chain reaction [PCR] testing of rectal lesions preferred), syphilis (darkfield microscopy of lesion, if available, in addition to blood serology), and mpox. An anal Pap test should be performed as well if it has not been performed within the past 12 months. Antibiotic therapy for infectious proctitis should be given pending diagnostic study results (algorithm 1) (see 'Proctitis' above):

•For all patients with proctitis, we suggest treatment for gonorrhea and chlamydial infection (Grade 2C). Ceftriaxone intramuscularly as a single dose (500 mg for individuals <150 kg or 1 g for individuals ≥150 kg) and doxycycline (100 mg orally twice a day) for seven days is the typical regimen.

•For patients who present with perianal or mucosal ulcers, we suggest treatment for HSV infection as well (Grade 2C). Valacyclovir 1 gram orally twice a day for 7 to 10 days, famciclovir 500 mg orally twice a day for 7 to 10 days, or acyclovir 400 mg orally three times a day for 7 to 10 days are typical regimens. Longer courses may be necessary in patients with HIV or who do not have resolution of symptoms at the conclusion of treatment.

•For patients who present with perianal or mucosal ulcers and/or a bloody rectal discharge, we suggest treating for lymphogranuloma venereum if they have HIV or have a positive rectal chlamydia NAAT (Grade 2C). This entails extending the doxycycline course to three weeks.

All patients with a positive diagnostic study for HSV infection (PCR or culture) or syphilis (blood serology and darkfield microscopy of lesion, if available) should be treated for the appropriate infection. (See "Treatment of genital herpes simplex virus infection" and "Syphilis: Treatment and monitoring".)

●Perianal abscess or anal fistula − Perianal abscess presents with pain, bleeding, and/or discharge, especially with defecation, and may be recurrent. Tenderness and submucosal fullness are present on digital rectal exam. Anal fistula presents as a “non-healing” perianal abscess or with chronic purulent discharge. Discharge or a fistula tract may be visible in the perianal area. The diagnosis of perianal abscess is suggested by physical examination and confirmed by transrectal ultrasound or pelvic MRI scan (with and without contrast) showing a cystic lesion followed by incision and culture of its contents. (See 'Perianal abscess/anal fistula' above.)

●Anal warts or dysplasia − Anal warts and dysplasia are generally asymptomatic and may coexist in a patient. They vary considerably in number and size, appearing as skin-colored papular lesions that may be visible on external rectal exam. Digital rectal exam is usually normal, and anoscopy may show white papular mucosal lesions, which represent internal warts. (See 'Anal warts/dysplasia' above.)

●Anal cancer − Anal cancer presents with rectal bleeding and/or pain associated with defecation. The stool caliber may be reduced in size, and there may be a recent history of weight loss. External rectal exam is generally normal, and a nontender firm mass is often detectable on digital rectal exam. The diagnosis is suggested by physical examination and confirmed by transrectal ultrasound or pelvic MRI scan (with and without contrast) followed by biopsy. (See 'Anal cancer' above.)