Differentials
Genital herpes
SIGNS / SYMPTOMS
There may be a history of fever, genital blisters or sores, and lymphadenopathy with first episode herpes simplex.
The patient may describe previous episodes of genital ulceration.
On physical examination there are typically multiple, painful vesicular or ulcerative lesions on or around the genitals or rectum.
INVESTIGATIONS
If lesions are present, clinical diagnosis should be confirmed by swabbing lesions for herpes simplex virus (HSV) culture or HSV polymerase chain reaction (PCR).[8]
Because of the higher sensitivity of PCR, this is the preferred test when available.[8]
Glycoprotein G-based type-specific serology may be indicated in certain patient groups and can differentiate between infection with HSV-1 and HSV-2.[8]
Chancroid
SIGNS / SYMPTOMS
Characterised by painful genital ulcers and painful inguinal lymphadenopathy. Lesions of primary syphilis are typically not painful.
Usually occurs in discrete outbreaks.
On physical examination there may be an erythematous papule, pustule, or painful ulcer, as well as painful unilateral inguinal lymphadenopathy (bubo formation), which may rupture.
INVESTIGATIONS
Haemophilus ducreyi is identified on specialist culture medium, which is not widely commercially available and has a sensitivity of <80%.[8]
Polymerase chain reaction testing is up to 100% sensitive but is not universally approved.[78][79]
Therefore a positive diagnosis of chancroid is suggested by the presence of one or more painful genital ulcers with no evidence of syphilis or herpes simplex virus.[8] Regional lymphadenopathy is also confirmatory, if present.[8]
Primary HIV infection
SIGNS / SYMPTOMS
Not preceded by genital ulceration.
However, genital ulceration may be present at the same time as primary HIV infection and the rash associated with the ulceration.
INVESTIGATIONS
Laboratory tests positive for HIV, including antigen (P24 antigen) tests.
Other acute viral exanthems
SIGNS / SYMPTOMS
Not preceded by genital ulceration.
INVESTIGATIONS
Laboratory tests positive for specific virus.
Scabies
SIGNS / SYMPTOMS
Skin lesions are usually pruritic.
Typical distribution: inter-digital, wrists, nipples, ankles, buttocks.
INVESTIGATIONS
Diagnosis is usually clinical, but skin scrapings and microscopy for Sarcoptes scabiei may be performed.
Eczema
SIGNS / SYMPTOMS
Skin lesions are usually absent on palms and plantar aspects of feet.
Not associated with signs of systemic infection.
INVESTIGATIONS
Diagnosis is usually clinical.
Skin biopsy can be undertaken to confirm diagnosis.
Psoriasis
SIGNS / SYMPTOMS
Skin lesions are usually absent on palms and plantar aspects of feet.
Not associated with signs of systemic infection.
INVESTIGATIONS
Diagnosis is usually clinical.
Skin biopsy can be undertaken to confirm diagnosis.
Lichen planus
SIGNS / SYMPTOMS
Skin lesions are usually absent on palms and plantar aspect of feet.
Not associated with signs of systemic infection.
INVESTIGATIONS
Diagnosis is usually clinical.
Skin biopsy can be undertaken to confirm diagnosis.
Genital warts
SIGNS / SYMPTOMS
Pink lumps, in genital and/or peri-anal skin and mucous membranes. Not necessarily confined to opposing membranes.
Not associated with other signs of secondary syphilis (rash, constitutional symptoms, generalised lymphadenopathy).
INVESTIGATIONS
Diagnosis is usually clinical.
Exclusion of syphilis (negative syphilis serology).
Alzheimer's dementia
SIGNS / SYMPTOMS
Progressive dementia.
No specific differentiating symptoms and signs compared with neurosyphilis.
Less likely to have a history of possible signs and symptoms of earlier stages of syphilis infection.
INVESTIGATIONS
Exclusion of syphilis (negative syphilis serology).
Vascular dementia
SIGNS / SYMPTOMS
Progressive dementia.
Multi-infarct dementia often associated with other evidence of arteriopathy.
Less likely to have a history of possible signs and symptoms of earlier stages of syphilis infection.
INVESTIGATIONS
Exclusion of syphilis (negative syphilis serology).
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