Indian Journal of Dermatopathology and Diagnostic Dermatology

: 2019  |  Volume : 6  |  Issue : 1  |  Page : 42--44

A curious case of vanishing pigmented spots resembling lentigines

Meenakshi Batrani1, Arshdeep1, Asha Kubba1, M Ramam2,  
1 Delhi Dermatology Group, All India Institute of Medical Sciences, New Delhi, India
2 Department of Dermatology and Venereology, All India Institute of Medical Sciences, New Delhi, India

Correspondence Address:
Dr. Meenakshi Batrani
10, Aradhana Enclave, R. K. Puram, Sector 13, New Delhi - 110 066


Exogenous pigmentation due to arthropods or coloring agents/dyes may be mistaken for melanocytic lesions. Dermoscopy is a useful tool for the evaluation of pigmented lesions. We discuss the dermoscopic and histopathological features in a case of pigmented spots mimicking lentigines caused by burrowing bug and review the pertinent literature on exogenous pigmentation.

How to cite this article:
Batrani M, Arshdeep, Kubba A, Ramam M. A curious case of vanishing pigmented spots resembling lentigines.Indian J Dermatopathol Diagn Dermatol 2019;6:42-44

How to cite this URL:
Batrani M, Arshdeep, Kubba A, Ramam M. A curious case of vanishing pigmented spots resembling lentigines. Indian J Dermatopathol Diagn Dermatol [serial online] 2019 [cited 2022 May 27 ];6:42-44
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Cutaneous pigmentation due to arthropods or coloring agents/dyes is uncommonly reported. However, the transient nature of pigmentation might account for underreporting of such cases. The few cases documented in the literature are mostly of the acral lesions masquerading as acral melanoma.[1],[2],[3] Rarely, pigmented spots, caused by burrowing bug (Cydnidae), have been cited, which may resemble lentigines.[4],[5] Dermoscopic features have been documented in some of the recent reports of exogenous pigmentation, particularly those simulating acral melanoma; however, there is still a paucity of literature in this regard. Histological features have rarely been studied as the diagnosis can usually be made clinically in most of the cases. Herein, we describe, the hitherto, undocumented dermoscopic and histopathological findings, in a case of pigmented spots mimicking lentigines caused by burrowing bug.

 Case Report

A 7-year-old girl presented with sudden eruption of four asymptomatic brown-black spots, one each on the right side of the neck [Figure 1]a, lower back [Figure 1]b, ventral aspect of left arm, and forearm, 4 days ago. The lesions were sharply circumscribed, variegated brown-black, round or streaky macules, approximately 4 mm in diameter. The two lesions on the arm and forearm were present, reciprocally on each side of elbow, resembling the “kissing” lesions of an insect dermatitis. On dermoscopy, lesions were brownish-orange with superimposed irregular darker streaks [Figure 2]a and accentuation in a vaguely rhomboidal pattern [Figure 2]b. The normal reticular pigmentary network of the skin was noticeable in the background, on higher magnification [Figure 2]b. The lesion on the back showed two blackish-orange follicular openings [Figure 2]b. The lesion on the back was biopsied.{Figure 1}{Figure 2}

Histopathology showed brownish-orange discoloration of stratum corneum and of keratin within the follicular ostium [Figure 3]a. Epidermis exhibited pallor, isolated necrotic keratinocytes, and focal confluent necrosis [Figure 3]b. Mild perivascular lymphocytic infiltrate was seen in papillary dermis. No dermal pigment was identified, and periodic acid–Schiff, Masson-Fontana, and Perl's stains were negative.{Figure 3}

During our initial clinical assessment of the patient, we considered a clinical diagnosis of lentigines, which was excluded on biopsy. All spots cleared spontaneously within a week. Based on histopathological features and spontaneous disappearance of lesions, a diagnosis of exogenous pigment was made. Both parents and child denied application of any topical medication or cosmetic product. Further questioning revealed that the spots developed suddenly after a visit to a wild life sanctuary during the rainy season, corroborative of exposure to either arthropod or contact with an unknown plant resin. Although the precise cause could not be elucidated with certainty, the presence of kissing lesions was strongly indicative of arthropod exposure. A literature search of all arthropod-related causes revealed that our case bore striking clinical resemblance to cases of pigmentation caused by burrowing bug, reported from the same geographic area.[4],[5]


There have been few reports of exogenous pigmentation due to arthropods or coloring agents published in the literature. Arthropod-induced pigmentation is caused by a defensive secretion released by the arthropod rather than by its bite. Most commonly implicated arthropod is millipede, with majority of the cases being reported from Brazil;[6] while there have been a single case series of four patients due to darkling beetle from Tunisia[7] and two case series, both from India, of four and two patients, respectively, due to burrowing bug.[4],[5] Besides, three cases, each attributed to a dye including black rubber,[1] black walnut,[2] and para-phenylenediamine,[8] have been cited. Most of the cases have been observed on feet, simulating acral melanoma,[1],[2],[3],[7],[8] except for an occasional case occurring at other sites, due to millipede[6] and burrowing bug.[4],[5]

In our patient, pigmentation due to burrowing bug was considered the most plausible diagnosis because of several clinical and epidemiological similarities, with the previously reported cases by Malhotra et al.[4] and Laad et al.[5] Similar to the present case, both these previous reports have also been from India. Patients present, particularly during rainy season, with sudden appearance of asymptomatic pigmented spots, which clear spontaneously. Akin to most of the arthropod-related pigmentation, there is a predilection for sole, but involvement of palms, chest, and neck has also been observed. The pigmented spots are small pinpoint to few millimeters in size, grouped or reciprocal macules, showing streaky shapes and tapering edges. Widespread lesions may simulate petechiae due to dengue, which is also prevalent in rainy season in the same geographic distribution, while a few scattered lesions may be mistaken for eruptive lentigines.[4],[5]

The pigmentation caused by other arthropods and due to coloring agents tends to involve larger areas of sole or toes, thus resembling acral melanoma or gangrene, unlike the small spots of burrowing bug resembling petechiae or lentigines. Millipede-related lesions are usually associated with symptoms such as erythema, pain, burning sensation, swelling, and paresthesia[3],[6],[9] and so are more easily recognized. Contrarily, no symptoms have been described in the lesions caused by burrowing bug[4],[5] and darkling beetle;[7] therefore, the inciting event may go unnoticed, as in our patient.

To the best of our knowledge, dermoscopic findings have been illustrated in only six previously published case reports of exogenous pigmentation, comprising nine patients, all on acral location, caused by arthropods including millipede[3],[6] or darkling beetle,[7] and dyes including black walnut, black rubber, and para-phenylenediamine.[1],[3],[8] A parallel ridge pattern, which is considered to be a characteristic dermoscopic feature of acral melanoma, has been described in seven out of these nine cases.[1],[3],[7],[8] Of all the arthropod-related pigmentation, histopathological features have been evaluated only in a single case series of four patients due to darkling beetle,[7] whereas a biopsy was performed in all three cases of dye-related exogenous pigmentation.[1],[3],[8] Interestingly, it is only in pigmentation due to darkling beetle that the exogenous pigment was identified within stratum corneum, while in all dye-related cases, histopathology failed to demonstrate the pigment, as it was likely dissolved during tissue processing.

Dermoscopic and histopathological features for burrowing bug pigmentation have not been delineated previously. In the present case, brownish-orange color observed clinically was attributable to discoloration of stratum corneum seen histopathologically. Biopsy also demonstrated discolored keratin plug within follicular ostium corresponding to dark follicular openings seen on physical examination and on dermoscopy. Analogous to our case, pigment accentuation within eccrine duct openings has been described on dermoscopy, in a case of exogenous acral pigmentation due to black walnut.[2] Dermoscopic findings of irregular streaks and pigment accentuation forming vaguely rhomboidal pattern in our case could possibly be due to the accumulation of exogenous pigment within the crypts in between the epidermal ridges and along the surface markings. It is key to note that this irregular pattern was superimposed on the normal reticular pigmentary network visualized in the background. These findings are unlike the dark brown regular reticular pattern of lentigo simplex and irregular pigmentary network characteristic of atypical melanocytic lesions, including dysplastic nevi and melanoma.


Clinical and dermoscopic findings in exogenous pigmentation may simulate melanocytic lesions; therefore, awareness, detailed clinical history, and dermoscopic evaluation are important to avoid misdiagnosis and unnecessary procedures. The clues to burrowing bug-induced pigmentation are occurrence during rainy season in India, asymptomatic spots of sudden onset with spontaneous clearing, grouped or reciprocal lesions of few millimeters in size, streaky shape, tapering edges, and brownish-orange hue.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.


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