Keratotic Spicules in Lichen Scrofulosorum: A Novel Dermoscopic Clue

Introduction

Lichen scrofulosorum (LS) is a rare form of tuberculids, a group of cutaneous tuberculosis caused by a type IV hypersensitivity response to Mycobacterium tuberculosis or its fragments. It most commonly affects immunocompetent children with either pulmonary or extrapulmonary tuberculosis. Dermoscopic findings of LS are rarely reported in the literature. Herein, we report a novel dermoscopic feature of LS in a young female.

Case Presentation

A previously healthy 36-year-old female was referred to us with a 4-month history of asymptomatic generalized papular rash. Examination showed multiple skin-colored-to-erythematous pinhead-sized follicular papules, isolated as well as coalescing to form annular plaques. The lesions were distributed bilaterally and symmetrically on the neck, trunk, abdomen, and upper limbs (Figure 1). Close inspection revealed numerous millimetric filiform keratotic spicules on the trunk (Figure 1C). Dermoscopy revealed keratotic cone-shaped and filiform spicules (Figure 2A–C). Other features included follicular plugs, perifollicular erythema, hemorrhagic crusts, and diffuse and perifollicular concentric white scales (Figure 2). Physical examination revealed bilateral firm, tender, non-fistulized cervical lymph node enlargement. The initial suspected diagnoses were folliculotropic mycosis fungoides associated with Hodgkin lymphoma and LS associated with tubercular lymphadenitis. On inquiry, the patient confirmed non-pasteurized milk consumption. She also reported night sweats and unintentional weight loss over two months. She had no personal or family history of tuberculosis. The Mantoux test was strongly positive, showing an induration of 35 mm. A lymph node biopsy revealed caseating granulomas on histopathology, consistent with tuberculosis. Histology of the papular eruption showed non-caseating epithelioid cell granulomas in the upper dermis. Special staining and tissue culture of a skin sample were both negative for Mycobacterium tuberculosis. The final diagnosis retained was LS with cervical tubercular lymphadenitis.

Figure 1.

(A,B,C) Clinical presentation of multiple skin-colored-to-erythematous follicular papules isolated and grouped in annular plaques over the neck, trunk, and abdomen.

Figure 2.

(A,B,C,D) Dermoscopy of papular rash revealed the presence of filiform hyperkeratotic spicules (black arrow), perifollicular erythema (green arrow), concentric and diffuse white scales (yellow arrow), follicular plugs (white arrow), and hemorrhagic crusts (red arrow).

Conclusion

The dermoscopic features of LS are poorly documented in the literature. The first description by Jassi et al. reported perifollicular dots, follicular plugs, and white scales [1]. Since then, several studies have examined dermoscopic aspects of LS. The most frequently reported findings include follicular plugs, white-to-brown globules or clods, white scales, perifollicular pallor, and erythema [1–3]. Our observation aligns with previously reported dermoscopic features and additionally reveals a novel finding: keratotic follicular spicules. Keratotic spicules have been associated with a range of etiologies. Neoplastic causes include multiple myeloma, where they are regarded as paraneoplastic signs, and folliculotropic mycosis fungoides, in which they may represent an early clinical or trichoscopic manifestation [4,5]. Infectious associations include human immunodeficiency virus infection and Demodex folliculorum infestation [6]. Finally, drug-induced cases have been described with acitretin, cyclosporine, and sorafenib. Several hypotheses have been proposed to explain their pathogenesis. In cases of plasma cell dyscrasias, deposition of dysproteins and cryoglobulins within the follicular infundibulum may lead to the characteristic spiky presentation [4]. In folliculotropic diseases, such as folliculotropic mycosis fungoides and LS, a localized inflammatory response targeting the follicular epithelium may induce reactive follicular hyperkeratosis, culminating in spicule formation.

In summary, our case expands the dermoscopic spectrum of LS by identifying keratotic follicular spicules, a feature previously reported in neoplastic, infectious, and drug-induced conditions.