Diagnosis : Steatocystoma Multiplex

Histology revealed a collapsed cyst in the dermis. The cyst wall was lined by multiple layers of stratified squamous epithelium [Figure 3]. Lobules of sebaceous glands could be seen in the wall of the cyst. The luminal surface of the cyst wall revealed homogeneous eosinophilic cuticle at foci [Figure 4].

Discussion

Steatocystoma multiplex (sebocystomatosis) is an autosomal dominant condition ^[1] that usually presents in adolescence. It is characterized by multiple, yellowish or skin-colored, dome-shaped nodules and cysts over the trunk, proximal extremities, and the face. However, acral distribution has also been reported. ^[2] The common sites of involvement are the chest and the arms, but these nodules can occur anywhere in the body. Sometimes, the condition can manifest as a solitary lesion, when it is called steatocystoma simplex.

These papules have to be clinically differentiated from other cysts. Eruptive vellus hair cysts are commonly found on the chest. Vellus hair cysts are reddish brown in color and may be associated with itching. Epidermoid cysts and occasionally, vellus hair cysts may have a black punctum. Trichilemmal cysts are more common on the scalp. ^[3],[4]

As the clinical features are variable, diagnosis may be difficult and require biopsy to be confirmed.

Steatocystoma multiplex and simplex arise from the ducts of sebaceous glands. ^[5] Histologically, these cysts are characterized by folded and crenated cyst walls that are lined by several layers of stratified squamous epithelium with wavy eosinophilic cuticles towards the luminal surface. ^[6] In atrophic areas, the lining may be one to three layers of flattened squamous epithelium. The diagnostic feature is the presence of lobules of sebaceous glands, which are either close to or seen within the lining epithelium. Occasionally, the lining of the cyst wall may contain macrophages. ^[1] Sabater-Marco et al. have reported the presence of smooth muscles in the cyst wall. ^[7] These cysts are usually empty as the predominantly lipid contents are washed away during the processing of the biopsy specimen. Uncommonly, homogeneous, light-staining, eosinophilic contents and vellus hairs may be visualized in the cavity of the cysts. Steatocystoma has to be differentiated histologically from trichilemmal cysts [Figure 5], eruptive vellus hair cysts [Figure 6], and infundibular cysts [Figure 7].

[Table 1] gives the salient features of different types of cutaneous cysts.

Steatocystoma is considered as forme fruste of pachyonychia congenita II and has been reported to be associated with mutations of keratin 17 gene in familial disease cases. ^[8],[9],[10] Steatocystoma has been found in association with various conditions like multiple keratoacanthomas, rheumatoid arthritis, hyperkeratotic lichen planus, hidradenitis suppurativa, acrokeratosis verruciformis of Hopf, ichthyosis, koilonychias, and bilateral preauricular sinuses. ^[11],[12]

Various modalities of treatment such as surgery, laser, and cryotherapy have been employed in treating this condition. Most of the surgical techniques involve excision of the cyst in toto or decapitation of the cyst, extirpation of its contents, and removal of the cyst wall. Cysts are opened by perforating the cysts with a needle tip, or by stab incision with a surgical blade no. 11, or by electrocautery, or by CO ₂ laser. ^{[13],[14],[15],[16],[17],[18]} The contents are then expressed out and the cyst wall removed or destroyed competely to prevent recurrence. Cyst walls can also be destroyed chemically or by CO ₂ laser or electrosurgery. ^[16] Isotretinoin (1 mg/kg/day) has been used with variable results in extensive steatocystomas. ^[19],[20]