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Erythema multiforme triggered by a spider bite in an adult female patient

Erythema multiforme (EM) is an immune-mediated condition characterized by erythematous plaques or papules that evolve into targetoid lesions distributed mostly on the distal parts of the extremities [1,2]. EM is due to an infection in more than 90% of cases particularly herpes and Mycoplasma infections. Drug intake is implicated in fewer than 10% of cases [1]. EM may also be caused by fungal infections, neoplasms, connective tissue disorders, or it may be idiopathic [2]. Here we report a patient presenting with EM lesions following a spider bite.


INTRODUCTION
Erythema multiforme (EM) is an immune-mediated condition characterized by erythematous plaques or papules that evolve into targetoid lesions distributed mostly on the distal parts of the extremities [1,2]. EM is due to an infection in more than 90% of cases particularly herpes and Mycoplasma infections. Drug intake is implicated in fewer than 10% of cases [1]. EM may also be caused by fungal infections, neoplasms, connective tissue disorders, or it may be idiopathic [2]. Here we report a patient presenting with EM lesions following a spider bite.

CASE REPORT
A 26-year-old female patient, with no history of recurrent infections, presented with an acral rash that appeared 5 days after being bitten by a small and shiny blackcolored spider on the trunk that she saw but she did not capture it. Physical examination revealed targetoid acral papules (Figs. 1 and 2) with no mucosal involvement and an inflammatory plaque under the right breast centered by two necrotic bullous lesions (Fig 3). General laboratory analysis was negative. Serological detection tests for Mycoplasma pneumoniae, anti-HIV antibodies and anti-HSV type 1 and 2 antibodies of both immunoglobulin (Ig) M and Ig G types were negative. We imputed the spider bite as the cause of EM based upon the clinical history and the laboratory tests that failed to implicate another cause of EM. The patient received topical Betamethasone Dipropionate 0,05% on the acral lesions and local wound care of the spider bite site, with a favourable course.

DISCUSSION
Spider bites are frequent, but most domestic spiders are not harmful for humans as they typically cause minor symptoms such as pruritic and small pink papules [3]. Rarely, fatal systemic immunologic reactions and severe local lesions occur [4]. These systemic reactions may result from some species commonly found in the Mediterranean basin. The most frequently involved spiders arise from the genus Loxosceles [5]. The local lesion of the spider bite is initially painless and may easily be overlooked by the patient [6]. Lesions may be mild, moderate, or severe depending upon the presence and degree of necrosis. Moderate lesions -as in this case-are the most common [7]. Apart from local lesions, the skin reaction to a spider bite may present as a maculopapular eruption over the entire body which has been reported in 5-32% of the published cases [2]. Acute generalized exanthematous pustulosis (AGEP) and pustular skin reactions have also been described [4,8]. A case of a drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome and few cases of cutaneous manifestations of systemic lupus attributed to a spider bite have also been reported [9,10]. EM is most likely an immune mediated mucocutaneous eruption that occurs in predisposed individuals [11]. EM usually appears in the setting of infection such as herpes simplex virus (HSV1 or HSV2) or Mycoplasma pneumoniae, but it may also be idiopathic [12]. Lesions mostly occur in a symmetric, acral distribution and may remain fixed at the same site for 7 days or more [2]. In our case, the clinical history combined with the typical skin lesions confirmed the diagnosis of EM. The laboratory tests eliminated other etiologies of EM. Hence, we could implicate the spider bite in its occurrence. There is one case of EM triggered by a spider bite reported in the literature [2]. The diagnosis was also established based on the clinical history and laboratory findings. Here, we present the second case.

CONCLUSION
We suggest that Loxosceles spider bites may cause erythema multiforme.

Consent
The examination of the patient was conducted according to the Declaration of Helsinki principles.