The patient was a 32-year-old woman with a 24-hour history of very pruriginous lesions on the hands, abdomen, neck, and thigh. The lesions were erythematous, and some were more edematous and others more eczematous. The only detail of interest was that she had been to the countryside the previous day (Fig. 1).

Figure 1.

Clinical images. A, Nonspecific erythematous lesions on the trunk. B, Lesions predominantly affecting the creases of the palm.

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Dermoscopy findings were remarkable for the presence of short multiple brownish-orange linear structures. Visual examination required a digital dermoscopy system, with magnifications of at least ×20-30. The structures corresponded to the characteristic urticating hairs of the pine processionary caterpillar (Thaumetopoea pityocampa) (Fig. 2). The history of contact with the countryside and the presence of urticating hairs were key to confirming the diagnosis in this case. The lesions resolved without sequelae after several days of treatment with oral antihistamines and topical corticosteroids.

Figure 2.

Dermoscopy findings. A, Low magnification image showing the dermatoglyphics of the palm with overlapping linear structures corresponding to the hairs of the pine processionary caterpillar. B, Detailed image of urticating hairs.

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The pine processionary caterpillar is one of the main causes of cutaneous-mucosal reactions to contact with Lepidoptera and is a growing public health problem. In its larval state, the caterpillar is covered with small urticating hairs, which cause lesions on contact with the skin. Owing to their “harpoon-like” morphology, with multiple spicules, these structures are able to remain attached to skin, animal hair, and even objects for long periods and can therefore cause symptoms without the need for contact with the pine forests they come from.1

The frequency of lesions resulting from this species is usually highest during the first quarter of the year, when mature caterpillars come down from the trees “in procession” in order to find a place to bury themselves.1

The lesions have many clinical manifestations, including involvement of the skin, eyes, and respiratory tract and anaphylaxis. The skin lesions have a nonspecific morphology in the form of papular dermatitis, urticaria, and even vesicles or blistering. They are more frequently found on exposed areas (neck and limbs), although they can also be found on covered areas and are usually accompanied by intense pruritus.1,2

Skin lesions have traditionally been treated with oral antihistamines, which are often combined with topical corticosteroids. Furthermore, there are reports of successful therapy with topical dobesilate.3

There are no pathognomonic clinical findings that enable us to diagnose the reaction to this species, except for direct visualization of the urticating hairs on the skin using dermoscopy. Nevertheless, both in the present report and in the literature, these hairs cannot generally be visualized directly using a manual dermatoscope, and a digital device is necessary to enable greater magnification (at least ×30).2

Therefore, pruriginous lesions on exposed areas should be viewed with a considerable degree of suspicion, and the patient should be asked about possible previous exposure to this caterpillar in order to identify the hairs that will confirm the diagnosis with the help of dermoscopy.1,2,4

The authors declare that they have no conflicts of interest.