eMedicine Specialties > Dermatology > Bacterial Infections

Chancroid: Differential Diagnoses & Workup

Author: Mark A Crowe, MD, Assistant Clinical Instructor, Department of Medicine, Division of Dermatology, University of Washington School of Medicine
Contributor Information and Disclosures

Updated: Aug 22, 2008

Differential Diagnoses

Behcet Disease
Fixed Drug Eruptions
Herpes Simplex
Lymphogranuloma Venereum
Syphilis

Other Problems to Be Considered

Extracutaneous Crohn disease

Workup

Laboratory Studies

  • The diagnosis of chancroid based solely on the ulcer's appearance is accurate only in 30-50% of cases. In areas of high prevalence, the accuracy for a clinical diagnosis of chancroid is as high as 80%; however, in areas where the disease is less common, the clinical basis for diagnosing chancroid leads to overdiagnosis. Considerable overlap exists between the major causes of GUD: herpes simplex, syphilis, chancroid, and, often, co-infection with 2 diseases at the same time. Co-infection with syphilis or HSV occurs in as many as 10% of patients. Realizing that no etiology can be found in 25-50% of all cases of GUD is important.
  • Gram staining may show gram-negative coccobacilli singly, in clusters, or in various morphological forms described as "schools of fish," "railroad tracks," or "fingerprints." The organisms are visualized extracellularly more often than intracellularly and tend to occur in close proximity to polymorphonuclear leukocytes.
    • Gram staining of an ulcer specimen is not highly specific or sensitive. Interpretation is hampered by polymicrobial contamination. However, slides with gram-negative coccobacilli in parallel rows or in a clustered school-of-fish pattern have been reported to have a sensitivity of 62% and a specificity of 99% for chancroid.
    • Direct microscopy should not be used in the routine diagnosis of chancroid.
  • Culture is now the accepted standard for chancroid diagnosis in most areas, but even in an experienced laboratory, it is only 60-80% sensitive. Numerous selective artificial media have been developed, but 2 media are commonly used. Nairobi medium consists of a biplate of (1) gonococcal agar base with 2% bovine hemoglobin and 5% fetal calf serum and (2) Mueller-Hinton agar with 5% chocolatized horse blood. Both media contain vancomycin (3 mcg/mL) and 1% CVA (ie, cephalothin, vancomycin, and amphotericin B) enrichment. The use of both media together increases the yield of positive cultures. Most H ducreyi organisms are resistant to vancomycin, but some strains are inhibited by its presence. Therefore, negative culture results in the setting of high suspicion should prompt screening for vancomycin-sensitive organisms.19
    • A simple, inexpensive medium containing gonococcal agar base supplemented with 5% Fildes' extract and unchocolatized horse blood or a medium containing 0.2% activated charcoal instead of fetal calf serum is a suitable alternative for diagnostic purposes in resource-poor countries.
    • H ducreyi is a fastidious organism. Patients' specimens must either be plated out directly on an appropriate culture medium or sent to the microbiology laboratory for culture as soon as possible. No widely available transport medium exists.20
    • Studies have shown cultures to be less sensitive in women than in men.
  • Purulent material aspirated from intact buboes is almost always sterile.
  • Polymerase chain reaction (PCR) amplification is replacing culture as the diagnostic test of choice in some major medical centers. PCR amplification using a variety of primers may provide a useful alternative to culture for the detection of H ducreyi. Although PCR assays perform well on samples prepared from H ducreyi cultures, they are less sensitive when used to test genital ulcer specimens.21
  • A multiplex PCR assay has been developed for the simultaneous amplification of DNA targets from H ducreyi, T pallidum, and HSV types 1 and 2 and appears more sensitive than standard diagnostic tests for the detection of these etiologic agents in genital ulcer specimens. The multiplex PCR assay has been developed but is not yet commercially available.22,23
  • Monoclonal antibody–based technology has the potential to provide a simple, inexpensive, rapid, and sensitive means of detecting H ducreyi in genital ulcer specimens, but no assay kits are commercially available.21
  • Serology has limited usefulness in the routine diagnosis of chancroid infection.
  • Tissue biopsy is not a recommended diagnostic method for chancroid but may be useful as a means to exclude malignancy in nonhealing or atypical ulcers.
  • Serologic tests for syphilis include the Venereal Disease Research Laboratory (VDRL) test, rapid plasma reagin (RPR) test, and a darkfield examination.
  • Tests for HSV include a Tzanck smear, direct fluorescence microscopy, and culture.
  • HIV testing should be performed in all patients who have genital ulcers caused by H ducreyi.
  • Patients should be retested for syphilis and HIV 3 months after the diagnosis of chancroid if the initial test results were negative.
  • Consider tests for other sexually transmitted diseases (STDs), including hepatitis B, Chlamydia trachomatis infection, and gonorrhea.
  • As PCR and other techniques become available, cultures may be indicated to obtain a specimen for antibiotic sensitivity testing.

Histologic Findings

Histologic features from a biopsy sample of a chancroid ulcer overlap significantly with those of syphilitic chancres. Lesions show 3 zones. The most superficial zone is narrow and consists of neutrophils, fibrin, erythrocytes, and necrotic tissue. The second zone is wider and contains newly formed blood vessels with marked endothelial cell proliferation. The lumina of many of these vessels are occluded, leading to thrombosis. The deepest zone is composed of a dense infiltrate of plasma cells and lymphoid cells. H ducreyi bacilli are seldom demonstrable on biopsy samples. Tissue biopsy is not a recommended diagnostic method for chancroid but may be useful as a means to exclude malignancy in nonhealing or atypical ulcers.

More on Chancroid

Overview: Chancroid
Differential Diagnoses & Workup: Chancroid
Treatment & Medication: Chancroid
Follow-up: Chancroid
Multimedia: Chancroid
References
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Further Reading

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Keywords

chancroid, HIV transmission, soft chancre, genital ulcers, STD, genital ulcer disease, GUD, Haemophilus ducreyi, H ducreyi, sexually transmitted disease, genital ulcer, bubo

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Contributor Information and Disclosures

Author

Mark A Crowe, MD, Assistant Clinical Instructor, Department of Medicine, Division of Dermatology, University of Washington School of Medicine
Mark A Crowe, MD is a member of the following medical societies: American Academy of Dermatology and North American Clinical Dermatologic Society
Disclosure: Nothing to disclose.

Medical Editor

Janet Fairley, MD, Professor and Head, Department of Dermatology, University of Iowa
Janet Fairley, MD is a member of the following medical societies: American Academy of Dermatology, American Dermatological Association, American Federation for Medical Research, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

Pharmacy Editor

Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Paul Krusinski, MD, Director of Dermatology, Professor, Department of Internal Medicine, Fletcher Allen Health Care, University of Vermont
Paul Krusinski, MD is a member of the following medical societies: American Academy of Dermatology, American College of Physicians, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

CME Editor

Joel M Gelfand, MD, MSCE, Medical Director, Clinical Studies Unit, Assistant Professor, Department of Dermatology, Associate Scholar, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania
Joel M Gelfand, MD, MSCE is a member of the following medical societies: Society for Investigative Dermatology
Disclosure: AMGEN Consulting fee Consulting; AMGEN Grant/research funds None; Genentech Consulting fee Consulting; Centocor Consulting fee Consulting; Centocor Grant/research funds None; Covance Consulting fee Consulting; Shire  Consulting

Chief Editor

Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

 
 
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