The biological agents used to treat autoimmune diseases increase the risk of opportunist infections. Strongyloides stercolaris is a human intestinal nematode that is very common around the world. Although it appears more often in tropical and subtropical regions, it may also be present in temperate zones. Infection is usually asymptomatic or with mild symptoms (pruritus, abdominal pain, diarrhoea) accompanied by eosinophilia (70%). In immunodepressed patients it may cause a disseminated infection known as potentially fatal hyperinfection syndrome.1

We present the case of a patient with rheumatoid arthritis under treatment with adalimumab, methotrexate and glucocorticoids who underwent infestation by Strongyloides.

A 43 year-old woman resident in Spain but who often travels to her native country, Bolivia. She has double seropositive erosive rheumatoid arthritis which has evolved over 10 years. She had been treated with methotrexate, leflunomide and several biological drugs (etanercept, certolizumab and tocilizumab) all of which were primarily or secondarily ineffective. Due to maintained and documented eosinophilia since 2010 (10%–14%) an etiological study was performed that gave negative results (parasites in stool, Strongyloides and Trypanosoma cruzi serology). Given the epidemiological risk factor and pharmacological immunosuppression empirical antihelminthic treatment was indicated with ivermectin (200μg/kg/day, 2 days). The patient did not attend the subsequent check-ups during several years. The patient is now under treatment with methotrexate, methylprednisolone 4mg/day and adalimumab 40mg/2 weeks. In January 2018 routine analysis found haemoglobin at 6.8g/dl with anaemic syndrome, due to which she was admitted to hospital. The cause was attributed to metrorrhagia in the context of a uterine myoma that was surgically resected. The anaemia persisted after a course of iron supplements and surgery. There was also moderate eosinophilia at 14% (1500×109 eosinophiles), which had increased over the last year. The patient also mentioned digestive symptoms with episodes of liquid diarrhoea without pathological products in recent months. A study of parasites in stool was performed that was negative, while serology was IgG positive for Strongyloides. Infection by the said parasite was assumed and treatment with ivermectin was prescribed (200μg/kg, repeated after 2 weeks). Once treatment had been completed the patient's digestive symptoms resolved, the levels of eosinophiles in the blood normalised and the anaemia was corrected.

3 cases are described in the Anglo-Saxon literature of patients with rheumatoid arthritis treated with anti-TNF alpha drugs who had infection by Strongyloides,2–4 together with one case that occurred during treatment with glucocorticoids and methotrexate.5 Although there is no study of Strongyloides prophylaxis in patients with rheumatic diseases under treatment with immunosuppressant drugs,1 cases such as this one mean that European rheumatology and tropical medicine societies should promote the study of parasites in stool and Strongyloides serology prior to starting immunosuppressant treatment in all patients from endemic areas and native patients with eosinophilia.6 It must be taken into account that negative serology in immunosuppressed patients does not rule out the diagnosis, and it is recommendable to monitor patients clinically to prevent relapses and evaluate possible repeat infections after travelling to their country of origin. Ivermectin at 200μg/kg/d over 2 days is usually the treatment of choice. However, in immunocompromised patients longer courses of treatment or combined therapy with albendazol may be necessary.7 Likewise, patients under treatment with biological agents who present symptoms similar to those described (eosinophilia whether accompanied or not by anaemia and digestive symptoms) should be subjected to differential diagnosis for infection by this parasite.6