The periscope sign as a new dermatoscopy finding to facilitate the diagnosis of furuncular myiasis

In this text, we introduce the ‘periscope sign’ as a novel dermatoscopic finding in furuncular myiasis. This clinical sign may aid in diagnosing this rare condition, particularly in patients with a history of travel to endemic areas.

A 65-year-old woman presented to our emergency consultation with painful nodules on her back.The patient reported that she returned to Switzerland about 5 days ago after travelling to Congo.While in Congo, she experienced several mosquito bites that initially caused intense itching, however, not on her back where the lesions were located, but rather on her legs.
Upon clinical examination, we observed multiple painful furunculoid nodules with central crateriform ulceration, resembling a volcano (Figure 1A), especially in a lesion where purulent discharge was also observed (Figure 1B).Dermoscopically, we also noted erythematous lesions with a central larval breathing hole, resembling a periscope (Figure 2A-B).Therefore, we would like to suggest the 'periscope sign' as a possible new dermatoscopic sign for easily identifying this condition.
In this case, we proceeded with the application of pure vaseline to occlude larval breathing (Figure 1C) and subsequently removed a total of eight larvae of varying sizes (Figure 3A).We then observed the larvae under a microscope at 10× magnification and could observe the larval breathing hole (Figure 3B, black arrow) and the presence of microspicules within the structure, allowing for a firm and stable anchorage in the subcutaneous tissue (Figure 3B, red arrow).This may explain the difficulty in removing these larvae, as they are well anchored in the subcutaneous tissue due to these spicules.The entomologist's assessment identified the larvae as Cordylobia anthropophaga.
Furunculoid myiasis is a form of dermatomyiasis in which fly larvae penetrate the skin and subcutaneous tissue, causing painful, suppurating nodules. 1,2Various fly species can cause furuncular myiasis, such as Dermatobia hominis in South America, C. anthropophaga in Africa, Cuterebra species in North America and Wohlfahrtia species in Europe or Pakistan. 3 ,4esions from C. anthropophaga are multiple, especially in areas covered by clothing.In fact, C. anthropophaga often deposits eggs on the ground or as more often seen in infections on humans, the eggs are deposited on clothes.Usually, in endemic areas, to prevent infections, it is necessary to iron clothes to prevent infection; however, if this is not done, the eggs can hatch, and the larvae, upon contact with the skin, can penetrate the subcutaneous tissue. 3,5n Switzerland, furuncular myiasis is rare and is often seen in patients returning from travels to these regions or in migrants originating from these regions of the world.Therefore, we observed this particularity dermoscopically, which we have nicknamed the 'periscope sign'.A periscope is an optical device that allows an observer to explore the entire horizon from a position where direct visibility is not possible, often used in submarines.This could be a fitting comparison, as the larva is located subcutaneously like a submarine, but to survive, it must expose part of its breathing hole to breathe.Furuncular myiasis is often a clinical diagnosis; however, a dermatoscope could be used to evaluate the lesions more closely.This could be a simple and easy-to-remember dermatoscope sign that would enable rapid recognition of this condition and appropriate therapeutic intervention.

Figure 1 Figure 2 Figure 3
Figure 1 Clinical presentation of myiasis; multiple painful furunculoid nodules with central crateriform ulceration (A), purulent discharge from a lesion (B), application of pure Vaseline on the lesions (C)