Differentials
Syphilis
SIGNS / SYMPTOMS
Characterised by a single non-tender ulcer as opposed to a painful ulcer.
INVESTIGATIONS
A positive non-treponemal test (e.g., rapid plasma reagin/Venereal Disease Research Laboratories titre, darkfield microscopy result) or a positive treponemal serology test.
Chancroid
SIGNS / SYMPTOMS
Characterised by a single deep ulcer, which is painful, as opposed to multiple painful ulcers with herpes.
INVESTIGATIONS
The presence of Haemophilus ducreyi on culture or polymerase chain reaction differentiates.
Lymphogranuloma venereum
SIGNS / SYMPTOMS
There is a lack of vesicles, with single or few ulcers and unilateral lymphadenopathy.
INVESTIGATIONS
A positive Chlamydia trachomatis nucleic acid amplification test and serovar typing for L1 to L3 help differentiate.
Mpox
SIGNS / SYMPTOMS
Patients typically present with a characteristic vesiculopustular rash that progresses in sequential stages that may involve the palms and soles. Prodromal symptoms may include fever, lymphadenopathy, backache, and myalgia. In the 2022-2023 clade II mpox outbreak, rash lesions were atypical, often localised to the genital, perineal/perianal, or perioral areas and not spreading further.
INVESTIGATIONS
Polymerase chain reaction of skin lesion material: positive for mpox or Orthopoxvirus DNA.
Contact dermatitis
SIGNS / SYMPTOMS
No differentiating signs and symptoms.
INVESTIGATIONS
Negative for HSV testing.
Behçet's disease
SIGNS / SYMPTOMS
Oral, eye, genital involvement. Patients with Behcet’s may also have oral ulcers and uveitis.
INVESTIGATIONS
Negative for HSV testing.
Rheumatological disease
SIGNS / SYMPTOMS
Exclusive oral involvement more likely.
INVESTIGATIONS
Elevated erythrocyte sedimentation rate and/or positive rheumatoid factor titre, antinuclear antibody titre.
Crohn's disease
SIGNS / SYMPTOMS
Exclusive oral involvement more likely in addition to gastrointestinal symptoms presence.
INVESTIGATIONS
Evidence on colonoscopy.
Ulcerative colitis
SIGNS / SYMPTOMS
Exclusive oral involvement more likely.
INVESTIGATIONS
Positive for ANA and evidence on colonoscopy.
Scabies
SIGNS / SYMPTOMS
May have disseminated skin involvement.
INVESTIGATIONS
Skin scraping for mites.
Fixed drug eruption
SIGNS / SYMPTOMS
History of medicine use.
INVESTIGATIONS
No differentiating test is available.
Squamous cell carcinoma
SIGNS / SYMPTOMS
Non-healing ulcerative lesions present.
INVESTIGATIONS
Skin biopsy reveals carcinoma.
Shingles on buttocks or lower extremities, or periorally
SIGNS / SYMPTOMS
Vesicles or pustules on an erythematous base present in both shingles and genital herpes. However, shingles typically erupts in a dermatomal distribution, with multiple lesions found over a wide distribution in a single dermatome, without extension over the midline.
INVESTIGATIONS
Polymerase chain reaction of vesicular or pustular fluid for varicella-zoster.
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