Hypersensitivity reaction to scorpion antivenom.

Sir,

A 21-year-old female patient was admitted to our hospital with generalized rash and severe itching since five days after being stung by a small yellow scorpion on her abdomen and receiving scorpion antivenom. According to her detailed history, on the day of the accident, she had presented to a local emergency department (ED) complaining fatigue and burning sensation at the site of the sting. The physician in the ED had intramuscularly administered one ampoule of polyvalent scorpion antivenin after skin test. However, the indication of the administration of antivenin was not clear. The antivenom used was purified polyvalent anti-scorpion serum produced by the Razi Vaccine and Serum Research Institute in Iran. The serum was prepared from the purified plasma of healthy horses immunized with venoms of the six dangerous scorpion species in Iran including Odontobuthus doriae, Mesobuthus eupeus, Androctonus crassicauda, Buthotus saulcyi, Buthotus sach and Hemiscorpius lepturus. This antivenin is usually presented in the 5-mL ampoules. Three hours after receiving the antivenom, she had developed the current symptoms which had improved with corticosteroids and antihistamines but had continued to relapse and remit. In our hospital, examination showed edematous, urticarial plaques intermixed with generalized flushing [Figures 1 and 2]. Neither lymphadenopathy nor discrete urticarial wheals were observed. The oral cavity and conjunctivae were not involved. The history, presentation and Naranjo adverse drug reaction probability score of nine[1] led to the diagnosis of immediate hypersensitivity reaction to scorpion antivenom. High doses of prednisolone and hydroxyzine were administered with sustained improvement of her signs and symptoms over 10 days.

Figure 1

Edematous, urticarial plaques and generalized flushing on the patient's back

Figure 2

Edematous, urticarial plaques on the dorsum of the patient's foot

Scorpion stings have local and systemic effects.[2345] Mild envenomations can be managed by supportive care. However, severe and life-threatening envenomations should be treated with scorpion antivenoms although the use of these products has potential risk of immediate and a more delayed-onset form of hypersensitivity reactions.[2678] This case shows that a hypersensitivity skin test is ineffective in predicting immediate-type hypersensitivity reactions in patients given scorpion antivenom.[6] Furthermore, this case highlights that hypersensitivity reaction to scorpion antivenom can present in the form of debilitating, prolonged cutaneous manifestations that may develop several hours after antivenom administration. This form of immediate hypersensitivity (delayed-onset and protracted) reaction to scorpion antivenom has not yet been reported in the literature. It is to be noted that antivenom was not indicated in this case in view of the patient's mild symptoms.[27]