A Case of Cutaneous Pili Migrans Caused by a Canine Hair

Dear Editor,

1.

Cutaneous pili migrans (CPM), or creeping hair, is a relatively rare skin condition characterized by a thin linearly migrating erythematous eruption with a slight pain by a fragment of hair [1]. Herein we report a case of CPM caused by an embedded dog hair.

A 22‐year‐old, female patient presented with slightly painful, linear erythema on the right sole (Figure 1a). One month before the current presentation, she noticed a minor skin wound on dorsal surface of fifth toe. The linear skin lesion had extended from the wound to right sole accompanied with erythema. Physical examination revealed a white, filamentous object with mild, surrounding erythema on right sole. The skin eruption was connected to the linear scale on the fifth toe, forming U‐shaped scale or purpura (Figure 1b). The filamentous object, which was easily extracted by forceps (Figure 1c), measured 11 mm in length and was clubbed at one end. After the filament was extracted, the lesion resolved. The filament was thought to be hair due to its shape; however, the patient had black hair and no poliosis. FTIR (Fourier‐transform infrared) analysis was performed to characterize the fibrous material based on its infrared absorption spectrum. Comparison of the obtained spectrum with a reference database revealed a close similarity to nail keratin, suggesting that the material was composed of keratin and was therefore likely to be hair (Figure 1d). To determine the animal origin of the hair, genetic analysis was performed. The DNA sequence of mitochondrial 12S ribosomal RNA from the filamentous material was 100% identical to that of Canis lupus (Eurasian wolf). An inquiry into the patient's living conditions revealed that the patient had a pet dog with white fur. Based on this finding, the present case was diagnosed as CPM caused by a dog hair.

FIGURE 1.

(a) The patient presented with a linear, erythematous lesion on the right toe. (b) The lesion was continuous with a linear scale on the fifth toe and formed a U‐shaped area of scales and purpura. (c) The filamentous object was easily removed using forceps. (d) FT‐IR spectrum analysis of the object revealed amide bonds, and a database analysis found the spectrum to be highly similar to that of nail keratin.

CPM and cutaneous larva migrans may present with similar linear skin lesions. The clinical symptoms, the direction of the migration, site of the skin eruption, and distribution of the lesion, are useful for differentiating these conditions [2]. That is, the presence of pruritus, multidirectional migration, and the occurrence of lesions on the trunk suggest creeping disease. Dermoscopy is also useful for visually identifying embedded hairs [3].

A notable feature of the present case was that the embedded hair was of pet origin, and that FTIR and DNA analyses were useful for its identification. To date, only three cases of CPM caused by an animal hair, including the present case, have been reported [4, 5]. All three reported cases were caused by dog hair. Regardless of breed, dog hair is generally finer than human hair and possesses densely packed, serrated cuticle scales. These characteristics may increase its propensity to penetrate and become embedded in the skin. In Japan, despite the overall number of pet animals remaining relatively stable, the number of pets kept indoors has increased. Therefore, CPM caused by pet hair should be included in the differential diagnosis of erythema migrans.

Ethics Statement

This study conforms with the Code of Ethics of the World Medical Association (Helsinki Declaration). All information pertaining to the patient has been anonymized.

Consent

Written informed consent was obtained from the patient for the publication of the details of this case.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.