The pathogenesis of these lesions has been extensively studied. Steatocystomas were initially thought to be sebaceous or retention cysts¹³. In 1964, Kligman and Kirschbaum¹⁴ included these as a variant of dermoid cysts because of the presence of both hair shafts and sebaceous lobules. Steatocystomas are now recognized as a nevoid or hamartomatous malformation of the pilosebaceous junction¹.

Steatocystoma multiplex is usually hereditary and it is inheirited as an autosomal dominant trait. However, it is nonhereditary for cases that the lesions are mainly limited to the scalp. The differences between typical steatocystoma multiplex and that limited to the scalp are presented in Table 2. In 1996, Lee et al⁶ reported on a case of sebocystomatosis that displayed multiple lesions of steatocystoma multiplex confined only to the forehead and frontal scalp together with congenital alopecia, and this was considered as a clinical variant of steatocystoma multiplex. Steatocystoma simplex, which is rarely found on the scalp, was first described as a distinct entity by Brownstein¹⁵ in 1982. It is similar to our case for the pathogenesis, the genetic propensity and the prognosis; however, steatocystoma simplex has a solitary nature (Table 2)^15-18. Lim et al¹² presented a patient with eruptive steatocystoma multiplex on the scalp. It was different from our case in that the lesions had appeared abruptly within a short period of time and the cysts showed an ovoid dilated cyst wall on histological study. Our case is educationally unique for the following points: (1) the presence of several cysts limited to the scalp, (2) no family history of similar lesions, (3) a late onset for the condition and (4) no congenital alopecia.

The causative factors of steatocystoma multiplex remain unclear, yet Setoyama et al¹¹ suggested that trauma, infection or immunological events might be responsible. Some authors have reported that steatocystoma multiplex has been associated with ichthyosis and koilonychia, pachyonychia congenita, acrokeratosis verruciformis of Hopf, hypertrophic lichen planus, hypohidrosis, hypothyroidism, hidradenitis suppurativa and hypotrichosis^4,18,19. For steatocystoma multiplex limited to the scalp, there have been no reports about specific causative factors and the relationship with other disorder, as was the case for our patient^3,4,7-12.

The clinical differential diagnosis of steatocystoma multiplex includes multiple epidermoid cysts, eruptive vellus hair cyst, neurofibromatosis, lipomas and xanthomatosis. A skin biopsy specimen from a representative lesion is diagnostic. The characteristic histopathologic finding of the disease is the presence of flattened sebaceous lobules close to the cystic wall. The wall is composed of stratified, squamous epithelium without a granular layer. There are acellular eosinophilic cuticles on the luminal side of the cyst wall and keratin, oil or hairs in the lumen².

Treatment of steatocystoma multiplex is largely symptomatic. Removal of these lesions can be successfully achieved with simple excision or drainage of the cyst materials. Inflamed lesions have been reported to respond to intralesional steroid injections, carbon dioxide laser, oral retinoids or cryotherapy². The lesions are typically asymptomatic, but they are often cosmetically disconcerting. Our patient declined further treatment after the diagnosis was made.