Differentials
Larva currens
SIGNS / SYMPTOMS
Caused by Strongyloides infection. Lesions typically found in perianal area, abdomen, and upper thighs, and last for only a few hours; characterised by a single track that advances rapidly by several centimetres an hour.[38]
INVESTIGATIONS
Strongyloides larvae seen on microscopic stool examination; positive Strongyloides IgG serology.
Gnathostomiasis
Fascioliasis
SIGNS / SYMPTOMS
Caused by Fasciola gigantica. History of eating raw leafy vegetables in Asia or Africa. Cutaneous track is deeply erythematous and tunnel-like.[41] Lesions cause burning pain and extend by 4 to 5 cm per day.
INVESTIGATIONS
Positive serological tests.
Extraction of fluke from advancing end of track.
Spirurina species infection
SIGNS / SYMPTOMS
Cases reported only in Japan.[42] Associated with eating raw seafood. Creeping eruption identical to CLM but usually single lesion present on abdomen.
INVESTIGATIONS
Positive serological tests.
Myiasis
SIGNS / SYMPTOMS
Characterised by cutaneous nodules often with central punctum. Patient frequently aware of movement within nodule. May migrate but typically no thin serpiginous track present. Lesions are not usually located on the feet.
INVESTIGATIONS
Extraction of fly maggot from skin lesion.
Loiasis
SIGNS / SYMPTOMS
History of exposure to mosquitoes in Central and West Africa.[40] Swelling is subcutaneous. Adult worms may migrate across conjunctivae.
INVESTIGATIONS
Identification of microfilariae on microscopic examination of blood sample; positive serological tests.
Creeping hair (cutaneous pili migrans)
SIGNS / SYMPTOMS
No association with travel. Typically involves slowly migrating skin fragment in upper dermis.[40] Pruritus not pronounced.
INVESTIGATIONS
Extraction of hair from advancing end of skin lesion.
Scabies
SIGNS / SYMPTOMS
Pruritus typically worse at night. In addition to papules or vesicles, burrows may be evident and will help to make the diagnosis. The wrists, ankles, palms, soles, interdigital spaces, axilla, waist, and groin are the most commonly affected sites. Patients will often report similar symptoms in family members or other close contacts.[43]
INVESTIGATIONS
Microscopy of skin scrapings may reveal mites, eggs, or scybala (mite faeces).
Cercarial dermatitis (schistosomiasis)
SIGNS / SYMPTOMS
Usually diffuse maculopapular rash. Skin lesions are non-migratory.[44] Rash typically appears within 24 hours of fresh-water contact in endemic area (Africa, China, the Philippines, Brazil, and other tropical countries in South America and the Caribbean).
INVESTIGATIONS
Diagnosis is initially clinical because egg laying has not yet begun; later, microscopy of stool and urine allows quantification of egg burden and Schistosoma species identification, and schistosomiasis serology will reveal antibodies against parasite antigens.
Herpes zoster infection
SIGNS / SYMPTOMS
Typical dermatomal distribution. Skin lesions are non-migratory and are characterised by vesicles that may coalesce and then crust. Usually more painful than pruritic.
INVESTIGATIONS
Smears of vesicle scrapings stain positive for varicella virus.
Jellyfish sting
SIGNS / SYMPTOMS
Association with swimming in the ocean. Skin lesions are non-migratory.
INVESTIGATIONS
Diagnosis is clinical.
Phytophotodermatitis
SIGNS / SYMPTOMS
Skin lesions are typically non-migratory and non-pruritic. In addition, they are usually pleomorphic and not just narrow serpiginous tracks.[45]
INVESTIGATIONS
Diagnosis is clinical.
Superficial thrombophlebitis
SIGNS / SYMPTOMS
Skin lesions are not usually migratory. Associated with pain and erythema but not pruritus. Clotted superficial vein usually palpable as a tender cord.
INVESTIGATIONS
Duplex ultrasound demonstrates lack of compressibility or intraluminal thrombus in the superficial veins.
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