Rheumatoid purpura associated with toxocariasis

Discussion

Henoch-Schönlein purpura is a systemic vasculitis; the dominant clinical manifestations include cutaneous purpura, arthritis, abdominal pain, and nephritis. Although the cause of the symptoms is unknown, Henoch-Schönlein purpura can be associated with toxic, infectious, or neoplastic conditions.¹ The association between Toxocara spp infection and vasculitis manifestations is unusual but has been previously described twice in cases of Henoch-Schönlein purpura.^1,2 In the case reported by Hamidou et al,¹ a male patient was hospitalized owing to a clinical spectrum of abdominal pain, fever, and arthritis, appearing within 1 week. He also had a purpuric rash on the lower limbs. Results of biologic investigations to identify a specific cause were all negative except for the T canis serology and blood hypereosinophilia. Henoch-Schönlein purpura spontaneously improved in 2 weeks. In this case, the clinicians decided not to prescribe an anthelmintic drug owing to the risk of worsening the immune vasculitis process by larval lysis.³ Some cases of systemic vasculitis associated with T canis infection were also reported.^4,5

The mechanisms involved remain poorly understood, but they probably involve an immune-mediated inflammatory response to the larvae migrating in tissues. Thus, it is hypothesized that parasitic antigens initiate the formation of immune complexes, whose localization in vessel walls either by deposition from the circulation or by in situ formation initiates the vasculitis. Otherwise, the most commonly encountered symptoms associated with toxocariasis are chronic skin disorders, in particular chronic urticaria.^6,7

Because human toxocariasis is a parasitologic dead end, neither adult roundworms nor eggs can be found in stools to make a direct diagnosis. Moreover, larvae are very rarely found in skin biopsies, and the procedure is too invasive for the severity of the disease. Consequently, the diagnosis is only indirect and 2 types of tests are available for the immunodiagnosis of toxocariasis: the enzyme-linked immunosorbent assay and the WB, both using T canis excretory-secretory antigens. Western blot is the more sensitive and specific of the 2 assays.⁸ The high specificity of the test is based on the distinction between the cluster of higher-molecular-weight bands, which is not specific and is suggestive of cross reactions with other helminthiasis, and the cluster of lower-molecular-weight bands, which shows a high level of specificity. Figure 1 shows an example of a positive WB result.

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Figure 1

Example of a postive Toxocara Western blot result

There are no consensus guidelines concerning the treatment of human toxocariasis associated with immune vasculitis processes. Spontaneous favourable evolution without anthelmintic therapy has been described.¹ The contribution of anthelmintic treatment remains controversial in vasculitis because the larval lysis could increase the immune vasculitis process. With other symptomatology, albendazole, diethylcarbamazine, or mebendazole gave satisfying results.³

The source of contamination is not always easy to identify. For example, in the case presented here the patient was not a cat or dog owner, but she was living in a rural area and reported frequent contacts with soil (gardening), which might have favoured exposure to Toxocara spp.

In all cases, prophylactic measures must be taken; they can prevent reinfection and must be explained carefully to patients. For example, dogs and cats must be treated by veterinarians; risk behaviour such as poor personal hygiene must be avoided; and dogs must be banned from public playgrounds in order to prevent infection of children from contaminated sand or geophagia.