The train tracks sign is a valuable skin marker of envenomations caused by caterpillarsA 64-year-old Caucasian woman sought a dermatological consultation 4 days after returning from a holiday in a rural area of the Southeast region of Brazil. She reported an acute painful sensation on her exposed chest after feeling something fall on her from an orange tree. Within a few minutes, the area became red, swollen, and severely painful. On examination, she had sequential petechial purpuric lesions, in a linear and parallel distribution pattern (Figure A). Dermoscopy of the lesion (DermaLite DL100™; 3Gen Inc., San Juan Capistrano, CA), demonstrated purpuric macules with overlying necrotic scales.
Sequential petechial purpuric lesions, with a linear and parallel distribution pattern. Upper left: Saturniidae caterpillar.
The skin appearance and the sudden pain after contact with a tree are strongly suggestive of caterpillar envenomation (erucism)1. Caterpillars of the Saturniidae family have hollow-body spines connected to venom glands1,2. When the spines penetrate the skin, they inject toxins and invoke the classical manifestations. The marks have a train tracks appearance and are caused by the distribution of the spines1,2.The combination of skin marks and intense local pain (sometimes with simultaneous lymphadenopathy), indicates a diagnosis of erucism2.
Saturniidae caterpillars (Figure A) are distributed mainly in tropical regions, but they can live in temperate climates1. Although caterpillars of other moth families (i.e., Megalopygidae) may also cause lesions with a similar appearance, the marks are not as clear as those of the Saturniidae family. Treatment consists of cold compresses and topical anesthetics, regardless of the moth species2,3.
REFERENCES
- 1 Haddad Jr V, Cardoso JLC, Lupi O, Tyring SK. Tropical dermatology: venomous arthropods and human skin: Part I: Insecta. J Am Acad Dermatol. 2012;67(3):331.e1-14.
- 2 Hossler EW. Caterpillars and moths: Part II. Dermatologic manifestations of encounters with Lepidoptera. J Am Acad Dermatol . 2010;62(1):13-28.
- 3 Haddad Jr V, Lastoria JC. Envenomation by caterpillars (erucism): proposal for simple pain relief treatment. J Venom Anim Toxins incl Trop Dis. 2014;20:21.
