A 22-year-old woman, with no significant past medical history presented to the clinic with a 2-month history asymptomatic skin eruption on her right upper extremity. The lesions. Over time, the lesions had growth in both number and extension. The patient denied any previous bleeding or trauma in the affected region.

Skin examination revealed the presence of reddish-brown macules strikingly distributed in a linear pattern on the anterior and inner regions of the patient's right arm and forearm (fig. 1). On closer inspection, such lesions were composed of pinpoint petechiae (fig. 1B1). Dermoscopy revealed the presence of red dots and lines over a homogeneous brown area (fig. 2).

Figure 1.

Clinical image.

(0.04MB).

Figure 2.

Dermoscopic image.

(0.06MB).

A slight perivascular lymphohistiocytic infiltrate with focal erythrocyte extravasation was identified, without other notable findings (fig. 3A and B). Perls’ staining revealed the presence of a few iron deposits on the superficial dermis (fig. 3C).

Figure 3.

Histopathological study. (A) Hematoxylin-eosin, ×10. (B) Hematoxylin-eosin, ×63. (C) Perls’ staining.

(0.18MB).

A complete blood test performed, including platelet count, coagulation study, and vitamin C levels, revealed no other pathological findings.

What is your diagnosis?

Unilateral linear capillaritis (ULC).

Given the nature of this entity, the absence of symptoms, and the tendency for spontaneous resolution, we decided to avoid treating the patient. The lesions disappeared within 6 months without leaving any scars or post-inflammatory hypo/hyperpigmentation.

ULC is a rare variant of pigmented purpuric dermatosis (PPD), first described by Riordan et al. back in 1992.1 ULC is characterized by the presence of purpuric macules of a linear or pseudo-metameric distribution affecting a single limb.2 Although ULC typically occurs on the lower extremities of young men, it can also affect the upper limbs.3

PPDs are disorders due to capillaritis of unknown origin. All different entities included in PPDs present similar histopathological findings, such as the presence of perivascular lymphocytic infiltrates, erythrocyte extravasation, and hemosiderin deposits.4 The clinical features determine the different subtypes of the disease.

The differential diagnosis of this entity includes other dermatoses of linear or Blaschkoid distribution, such as psoriasis, linear verrucous epidermal nevus, linear lichen striatus, linear lichen planus, some viral exanthems, unilateral nevoid telangiectasia, and serpiginous angioma. Additionally, other PPD variants—particularly lichen aureus—should be ruled out as it can clinically exhibit a linear or segmental morphology. In this regard, it would be interesting to find a dense band-like dermal infiltrate, separated from the epidermis by an unaffected papillary dermis area (Grenz zone).5 However, in our case, the rapid resolution of the lesions and the presence of vacuolar degeneration, along with a series of hemosiderophages, suggest ULC rather than lichen aureus.

As it happens in other PPD variants, topical corticosteroids have proven effective for treating pruritus. Psoralens and UVA phototherapy, ascorbic acid, rutin, and griseofulvin have also been used with variable effectiveness. The prognosis of ULC is good, usually resolving spontaneously in less than 2 years.1,3,5

In conclusion, a case of a rare PPD variant—ULC—has been described in a woman with an atypical location but with clinical, dermoscopic, and histological findings characteristic of this disease.

The authors made substantial contributions to the idea and design of the study, drafting and critical revision of the manuscript, approving its final version for publication.

None declared.

None declared.