Steatocystoma Multiplex

Introduction Steatocystoma multiplex (SM, also known as steatocystomatosis, sebocystomatosis, or epidermal polycystic disease) is a rare benign intradermal true sebaceous cyst of various sizes.[1,2] It is considered a nevoid or hamartomatous malformation of the pilosebaceous junction.[3] The classification of SM includes localized, generalized, facial, flexural, acral, syndromal, and suppurative types.[4] This review intends to draw attention to this unique dermatological condition. History The term SM translates to "a bag of fat." In 1873, SM was first described by Jamieson in a case with numerous cysts distributed throughout the body. The term 'steatocystoma multiplex' was coined in 1899 by Pringle.[4] In 1982, Brownstein described steatocystoma simplex as a distinct entity.[5] Epidemiology The exact prevalence of SM is not known in the general population, with no gender or ethnic predilection.[6] In acral subcutaneous SM, a female preponderance is reported.[7] The occurrence of SM is common in the second and third decades of life. However, the skin lesions can occur at any age, as evidenced by their occurrence at birth or as old as 78 years of age.[8] SM in four successive generations in the same family have been reported.[9] Aetiopathogenesis The exact pathogenesis of SM is not known. According to the retention cyst theory, an initial sebaceous duct blockage with a keratinous plug results in cyst formation. However, it fell out of favor, as on numerous occasions, researchers were not able to show the blockade histopathologically.[10] Kligman and Kirchbaum hypothesized that pluripotent ectodermal cells retain the embryonic capacity to form appendages or naevi rather than inclusion or retention cysts.[1] The keratin 17 gene (KRT17) encodes for a type 1 intermediate filament (K17) that is predominantly expressed in the hair follicles and sebaceous glands. The missense mutation of the K17 gene is associated with nevoid cyst formation in SM.[10,11] Most of the cases of SM are sporadic and are rarely inherited in an autosomal dominant trait that is linked to a mutation in exon 1 of keratin 17.[12] Other mutations rarely associated with SM include N92S, R94C, and R94H.[6] The different mutations can result in the same clinical phenotypes, whereas the same mutations can cause different clinical phenotypes.[13] Factors such as infections, trauma, or immunological episodes might be responsible as a trigger factor in SM.[3] Clinical features Clinically, SM presents as asymptomatic, numerous, round, smooth, firm, mobile, cystic papules, and nodules.[1,10] The lesions are uniform, with a size of a few millimeters to centimeters along the long axis.[14] The superficial lesions are yellowish, and deeper lesions tend to be skin-colored.[1] The fluid in SM is odorless, oily, clear or opaque, milky or yellow.[15] The overlying epidermal skin is often normal, with no central punctum.[1] SM can occur anywhere in the body but is more frequently seen in areas rich in pilosebaceous units such as the trunk (especially the presternal region), neck, scalp, axilla, proximal extremities, and inguinal region [Figures 1 and 2].[10]Figure 1: (a) Steatocystoma multiplex over the neck. Note the yellowish nature of the lesions (b) Steatocystoma multiplex over the posterior trunkFigure 2: Extensive steatocystoma multiplex over the anterior trunkSM can transform into steatocystoma multiplex suppurativum (SMS, also known as steatocystoma multiplex conglobatum) at any point in time during its natural course [Figure 3a].[16] It can have associated pain, pruritus, and pyrexia.[17] Cysts often become inflamed, rupture, and drain, resulting in scarring, thus sharing overlapping features with hidradenitis suppurativa. The secondary bacterial infection leads to malodourous discharge and abscess.[2,16]Figure 3: (a) A case of steatocystoma multiplex suppurativum. Note the simultaneous presence of active steatocystoma multiplex lesions along with scars clinically mimicking acne conglobata (b) Steatocystoma simplex in the shaft of the penisThe sporadic solitary tumor counterpart to SM is steatocystoma simplex [Figure 3b]. The atypical clinical presentations include giant SM, linear SM, palatal SS, and extensive calcification of SM.[1,12,18,19] Vulvar SM affecting the sexual activity of women is known.[20] SM of the scalp with concurrently acquired alopecia secondary to trichotillomania has been reported.[21] The occurrence of multiple SM is reported in a psoriasis patient on ustekinumab treatment.[11] Associations SM has been associated with hidradenitis suppurativa (HS), pachyonychia congenita, ichthyosis, koilonychia, acrokeratosis verruciformis of Hopf, hypotrichosis, hypohidrosis, hypothyroidism, hypertrophic lichen planus, multiple keratoacanthomas, rheumatoid arthritis, preauricular sinus, pili torti, pili canaliculi, neurofibromatosis 1, and polycystic kidney disease. Patients should be screened for any other ectodermal abnormalities.[14,15,22-24] Co-occurrence of SM with hidradenitis suppurativa, eruptive vellus hair cysts, trichofolliculomas, trichoepitheliomas, and trichoblastomas have been reported.[15] Syndromal associations include X-linked recessive Lowe syndrome, Gardner syndrome, Noonan syndrome, Alagille-Watson syndrome, and Favre-Racouchot syndrome.[4] Diagnosis Differential diagnosis SM is often confused with eruptive vellus hair cyst (EVHC), whose differences are mentioned in Table 1.[25,26] The other differential diagnosis of SM includes multiple epidermoid cysts, neurofibromatosis, xanthomatosis, lipomatosis, milia, follicular infundibular tumors, severe nodulocystic acne, pseudofolliculitis. The salient clinical and histopathological features of the diseases that can mimic SM and its variants are shown in Table 2. When the lesions are inflamed, folliculitis, acne conglobata, and hidradenitis suppurativa should be considered.[3,4,17,25,27]Table 1: Differences between steatocystoma multiplex and eruptive vellus hair cystTable 2: Characteristics of the differential diagnosis of variants of steatocystomaDiagnostic methods A diagnosis of SM should always be confirmed with histopathology. Histologically, the cysts are well encapsulated, the walls have several layers of epithelial cells that intricately fold and flattened sebaceous gland globules within or close to the cyst wall. A thick, homogenous, eosinophilic cuticle without an intervening granular layer lines the inside wall of the cyst and protrudes irregularly into the lumen [Figure 4a]. The lumen often contains oil, hair, and keratin.[1,10]Figure 4: (a) Cyst lining in a wavy, homogenous, eosinophilic horny layer with several layers of epithelial cells collapsed around the cystic space. Note the embedded lobules of sebaceous glands among the epithelial cells (H&E, 20x) (b) Dermoscopy showing the yellowish structureless area (Dermlite D4, polarized, original magnification x10)In immunohistochemistry, the inner epithelial lining of the cysts shows positive staining with calretinin, the upper layer cells in the upper cyst wall express keratin 17, and basal and suprabasal layers express keratin 14.[20,28] The fine needle aspiration cytology of the cyst fluid shows predominantly acellular, granular debris, crystalline structures, rare anucleated squamous cells, and cholesterol crystals.[29] Dermoscopy of SM shows yellowish structureless areas (corresponds to sebum contained in the cyst cavity) with diffuse margins [Figure 4b].[4] Mammographs typically reveal multiple oil cysts that have a central fat density. Ultrasound imaging shows multiple anechoic cysts with posterior acoustic enhancement.[6] Ultrasonography with color Doppler is a non-invasive tool that can differentiate SM and HS.[16] Magnetic resonance imaging shows hyperintense lesions.[30] Treatment The goals of SM management include a substantial reduction of cyst size, good cosmesis, and good patient satisfaction. Most of the time, patients seek medical advice for cosmetic reasons.[8] There is no specific gold standard treatment option, and it should be geared toward the patient's clinical presentation.[6] A wide variety of treatment modalities have been tried for SM.[8] The treatment response for this condition is generally not satisfactory.[17] The eventual recurrence of the lesions after treatment is the rule.[1] Surgical management includes simple aspiration with an 18-gauge needle, incision and expression of the cyst contents, and radiofrequency probe-mediated extrusion of the contents [Figure 5].[1,8] The use of tissue adhesives for skin closure following the surgical removal of the cyst has good efficacy.[31] For localized variants of SM, local destructive methods such as cryotherapy have been reported to be efficacious.[32] The complete surgical excision of the cysts followed by skin grafting has been tried in the past.[33] Tricarboxylic acid treatment of the cyst walls can be administered after the aspiration of contents.[34]Figure 5: (a) Extrusion of cheesy, oily material after a small nick in a lesion (b) Sac protruding out of the steatocystoma multiplexFor non-infectious inflammatory lesions, a short course of oral tetracyclines, topical benzoyl peroxide wash, or clindamycin might be considered. Systemic isotretinoin, due to its anti-inflammatory effect, decreases the size of pre-existing cysts and prevents the formation of new lesions.[35] However, some authors have reported worsening or exacerbating the condition in patients with SM and severe inflammation. Few have observed that systemic isotretinoin had no effect on non-inflamed lesions of SM. A combination of oral rifampicin and clindamycin has shown efficacy in the case of SMS.[36] The treatment with adalimumab in patients with coexistent SMS and HS has shown good efficacy.[2] Lasers are advantageous because they are minimally invasive. Ablative laser therapies, such as erbium: yttrium-garnet laser, fractionated and non-fractionated Co2 laser, have been tried.[37] A combination of two non-ablative lasers with complementary mechanisms, such as the 1550-nm fractionated Erbium-doped fiber laser that targets dermal cysts and the 1450-nm diode laser that targets abnormal sebaceous glands have shown dramatic improvement in a patient with recalcitrant SM.[38] The 1927-nm fiber-optic diode laser has demonstrated excellent clinical outcomes with minimal adverse effects in a patient with facial SM.[39] A summary of the treatment options for SM is mentioned in Table 3.[31,35,37-42]Table 3: Summary of various treatment modalities in steatocystoma multiplexConclusion SM should be considered as one of the differential diagnoses in patients with multiple asymptomatic intradermal cysts. Early disease recognition and appropriate counseling might help alleviate the psychological implications associated with the disease. It is a rare clinical entity with poor treatment outcomes. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.