Eruptive vellus hair cysts

ARTICLE

Comments

Eruptive vellus hair cysts (EVHC), first described in 1977 [1], most frequently occur in adolescence or early adulthood with multiple asymptotic flesh- or white-to-yellow coloured papulocystic lesions, 1 to 5 mm in diameter sometimes with an umbilicated or crusted surface. In most cases, the anterior chest wall, the abdomen and the extremities are involved, however, EVHC may also occur on the neck, the face [2] and even in a generalised distribution [3]. EVHC may occur sporadically or be inherited in an autosomal dominant pattern [4, 5] with males and females equally affected. In sporadic cases the age of onset of EVHC is 4 to 18 years, sometimes with an abrupt increase in the number of skin lesions in early adulthood. Most cysts show a tendency to regress spontaneously after some months to several years [1, 3, 6-8], but may also persist lifelong.

The differential diagnosis of EVHC includes a broad range of dermatoses, including steatocystoma multiplex (SM), as well as multiple epidermal (EC), trichilemmal (TC) or dermoid cysts (DC), closed comedones, acneiform eruptions and milia.

The most important of these differential diagnoses is steatocystoma multiplex (SM) which shares with EVHC the same clinical features as to morphology, predilection sites, age of onset and mode of inheritance. Therefore, EVHC and SM can only be differentiated by histological examination: vellus hair cysts are characteristically filled with laminated keratinous material and a varying number of vellus hair fragments, with a cystic wall lined by several layers of squamous epithelium, sometimes with a discrete granular layer [9]. In contrast, SM presents with an empty cyst due to an artificial loss of its content by the fixation process. In SM, the cyst is lined by a thin wall of stratified squamous epithelium without a granular layer; the horny layer is formed by a prominent, acellular, brightly eosinophilic cuticle with an undulant configuration. Occasionally, hair fragments mainly of the lanugo type have been observed in the cavity. A highly characteristic finding in SM is the presence of sebaceous elements adjacent to or within the cyst wall. Interestingly, some authors have described overlapping histological features of both EVHC and SM within one cyst [10-13] or the appearance of EVHC and SM in one patient [14-16].

Epidermal (EC) and trichilemmal (TC) cysts are other close differential diagnoses of EVHC. EC present clinically as slowly growing intradermal or subcutaneous tumours. Histologically, the wall of EC is composed of complete epidermis (squamous, granular and horny layers) and a cavity filled with horny material arranged in laminated layers. TCs are clinically nearly indistinguishable from ECs, but are less common, appear in about 90% of cases on the scalp and show histologically a cyst wall with distinct palisading of the peripheral cell layer, trichilemmal differentiation and keratinisation without formation of a granular layer as well as typical swelling of the cells close to the cavity [9].

Recently Tomkova et al. [17] have pointed out that assessment of the keratin pattern may aid in the differential diagnosis of EVHC, SM and other skin cysts. The comparison of the expression patterns of keratin 10 (K10) and keratin 17 (K17) in different types of cysts revealed an expression of K10 in EC, TC and SM, and an expression of K17 in TC, SM and EVHC. Thus the presence of K17 with the concomittant absence of K10 promises to be a diagnostic feature of EVHC.

Although the pathogenesis of EVHC has not been clarified yet, several pathological mechanisms have been put forward. It has been suggested that a developmental abnormality predisposes the vellus hair follicle in EVHC to infundibular occlusion [1, 6]. Cystic development may then follow due to retention of keratinous material and hair shafts and may be accompanied by secondary atrophy of the hair bulbs [1]. Kumakiri et al. [2] have proposed that EVHC may be pilosebaceous hamartomas with the potential to differentiate towards a vellus hair matrix and keratinocytes resembling the infundibular and isthmus portions of the outer root sheath. Referring to the close relationship between EVHC and SM, several authors have emphasised that the morphological features of the developing cysts depend on the structure from which they originate [15, 18]. Ohtake et al. [15], for example have proposed that both, EVHC and SM may result from a cystic change near the junction of the pilosebaceous duct. The two diseases may therefore rather represent a spectrum of the same disease process than separate entities. Whether it is in fact justified to lump EVHC and SM together as multiple pilosebaceous cysts (MPSC), is a matter of debate.

Until now, effective, safe and cosmetically satisfying therapeutic strategies are lacking. Incision and drainage as well as excision of the cysts have been applied but cause scarring. Dermabrasion is an interesting option but frequently limited, due to the extensive distribution of the skin lesions. Huerter et al. [19] have described the effective treatment of EVHC without scarring or recurrence of lesions using carbon dioxide laser vaporisation. Application of topical retinoic acid [20] and chemical peeling with 12% topical lactid acid [21] have been reported to be successful. Systemic treatment with vitamin A or isotretinoin has only been of minor benefit [22].

Accepted on 15/5/00

REFERENCES

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