Differential Diagnosis for Cross-Reaction with Quest Diagnostics Filariasis IGG4 AB Test

Given the patient's symptoms of small idiopathic fibrotic ulcers with firm edges that do not respond to standard antibiotics and fail to heal in a timely manner, the following differential diagnoses are considered for parasitic infections that could cross-react with the Quest Diagnostics Filariasis IGG4 AB test:

• Single Most Likely Diagnosis

  • Loiasis: This is due to the Loa loa parasite. The cross-reactivity and the presentation of skin lesions (Calabar swellings) in loiasis could explain the patient's symptoms and the potential for cross-reactivity with the filariasis test.

• Other Likely Diagnoses

  • Mansonelliasis: Caused by Mansonella species, this infection can present with skin lesions and could potentially cross-react with filariasis tests due to antigenic similarities.
  • Onchocerciasis: Although primarily known for causing river blindness, onchocerciasis can also lead to skin lesions and nodules. The Onchocerca volvulus parasite might cross-react with filariasis tests, given the relatedness of the parasites.
  • Strongyloidiasis: This infection, caused by Strongyloides stercoralis, can lead to skin lesions and might cross-react with filariasis tests, especially in cases of chronic infection.

• Do Not Miss Diagnoses

  • Toxocariasis: While less likely to cause the specific symptoms described, toxocariasis (caused by Toxocara species) can lead to visceral larva migrans and, in rare cases, skin manifestations. It's crucial not to miss this diagnosis due to its potential for severe complications.
  • Anisakiasis: Primarily a gastrointestinal infection caused by Anisakis larvae, anisakiasis can occasionally present with skin manifestations and should be considered due to its potential for severe allergic reactions and gastrointestinal complications.

• Rare Diagnoses

  • Dirofilariasis: Caused by Dirofilaria species, this infection is more commonly associated with dogs but can occasionally infect humans, leading to skin lesions or nodules. The potential for cross-reactivity with filariasis tests is low but should be considered in endemic areas or with relevant exposure history.
  • Capillariasis: This rare intestinal infection caused by Capillaria philippinensis can lead to severe complications, including malabsorption and potentially skin manifestations in rare cases. The potential for cross-reactivity is low, but the severity of the disease warrants its inclusion in the differential diagnosis.