An atypical mole

A 38-year-old woman undergoing annual dermatological follow-up for excision of a melanoma in situ 4 years previously presented with a cutaneous lesion of 2–3 days’ duration without known triggers. On examination, in addition to her multiple benign nevi, there was a blackish macule on the right abdomen (Fig. 1A, black arrow). Dermoscopy (Fig. 1B) revealed a tick approximately 5 mm in size, dark brown in colour, with black lines and four pairs of legs. The appearance was consistent with a bite from a Rhipicephalus sanguineus tick (dog tick). The patient admitted to owning a dog without regular veterinary care. When offered methods of removal, the patient refused traction and biopsy was offered. Histology (Fig. 1C and D) revealed a mild mixed inflammatory infiltrate in the superficial dermis and an external structure adjacent to the horny layer with an exoskeletal structure compatible with an ectoparasite.

Figure 1.

Clinical presentation at the time of diagnosis in the emergency room. (A) Blackish macule on the right abdomen (black arrow). (B) Dermoscopy showed a dark brown tick with black lines and four pairs of legs. (C) (haematoxylin–eosin, 4×) and D (haematoxylin–eosin, 20×). Histologically, in addition to a mild mixed inflammatory infiltrate in the superficial dermis, a structure was observed adjacent to the stratum corneum with an orange chitin exoskeleton and multiple internal organs compatible with an ectoparasite.

Microbiological examination confirmed the presence of Rhipicephalus sanguineus infected with Rickettsia conorii Mediterranean spotted fever (MSF) ribotype. With the diagnosis of incipient MSF, the patient was treated with doxycycline 100 mg every 12 h for 10 days. At the one-month follow-up, the patient was asymptomatic. Serology confirmed the presence of IgM against R. conorii.

Rickettsial infections and related infections (such as anaplasmosis, ehrlichiosis and Q fever) are caused by an unusual type of bacteria that can only live inside the cells of another organism (such as ticks or fleas).¹ Early detection is essential to avoid the consequences of delayed treatment.

Authorship

All authors had access to the data and played a role in writing this manuscript.

CRediT authorship contribution statement

• •

  Miguel Mansilla-Polo managed initial clinical diagnosis and treatment and contributed to the direction and development of this paper.

• •

  Vicent Martínez-Cozar directed the pathological study and supervised all the work.

Informed consent

Oral and written consent was obtained to publish this image.

Ethical approval

Ethics: procedures followed here were in accordance with the ethical standards of the responsible committee on human experimentation and with the Helsinki Declaration of 1975, as revised in 1983. We have not use patients’ names, initials, or hospital numbers.

Funding

This article has no funding source.

Conflicts of interest

The authors have declared no conflicts of interest.