NC is classified into two main types based on its clinical characteristics [3
]. The first type is non-pyogenic NC with acne-like characteristics. The second type is NC with cysts, papules, pustules, or abscesses that undergo morphological changes. The case described here, which is of the latter type of NC, involved a large cyst that recurred due to previous incomplete surgery. Additionally, the size of this cyst gradually increased due to a lack of sebum secretion due to postoperative invagination of the orifice. Furthermore, expansion of the skin lesions due to increasing size of the cysts results in an elevated risk of infection. Presumably, this increased infection risk and frequent periods of inflammation might therefore contribute to the development of large cysts.
Previously published reports of NC cases showed that this condition sometimes presents concurrently with epidermal or skin appendage tumors, such as epidermolytic hyperkeratosis, epidermal nevus, and eccrine nevus [4
]. Additionally, Engbers [6
] reported rare cases in which NC occurred concurrently with other skin lesions or certain types of internal abnormalities or ailments; he termed this condition "NC syndrome". NC syndrome belongs to the large category of epidermal nevus syndromes in which epidermal nevus appears concurrently with abnormalities of other body organs, such as neurological deficits (epilepsy and electrocardiogram abnormalities), skeletal abnormalities (scoliosis and spina bifida), and eye problems (congenital cataracts) [6
]. Physical examination and other laboratory test results indicated that the current case was not NC syndrome.
Histopathologically, NC is characterized by the presence of extensive and deeply stratified keratin in the epidermis. The invaginated epidermis is composed of various types of keratinocytes. It is important for NC to be clinically differentially diagnosed from acne vulgaris [3
]. Histopathological analysis reveals that the skin appendage tumors include dilated pore of Winer, pilar sheath acanthoma, and trichilemmal cyst [7
]. In the present case, histopathology showed that the large cyst was typical of those containing keratinized tissue. The histopathological findings in this case were almost identical to those of a sebaceous cyst.
Because of recurrent infections and cosmetic problems, NC poses a great challenge to clinicians, and the only effective treatment method is surgery. It is important for those with NC to maintain good hygiene, and antibiotics can also be used as a conservative method of treatment. As a localized treatment, retinoic acid can be used to induce the expansion and differentiation of keratinocytes, which would be effective for the elution of nevus. In addition, ammonium lactate lotion [1
] softens the epidermis, thereby promoting the excretion of nevus. Other available treatments include the mechanical removal of nevus, dermabrasion, or laser therapy. However, these methods cannot prevent recurrence of the lesion [3
] and surgical removal is the treatment of choice for NC. In cases involving a smaller area, the primary suture should be performed following resection. Cases with larger affected areas require staged excision or skin grafting. In some cases, reconstruction using a tissue expander would be helpful.
Due to a time-dependent increase in the risk of opportunistic infections, NC undergoes morphological changes to cysts, papules, pustules, or abscesses. Non-surgical supplemental treatment methods can be effective to a limited degree. Our case showed that large, multiple cysts could occur as one of the long-term complications of NC, and it also suggests the importance of radical resection for further invagination of the lesion. Besides, it also indicates that NC should be differentially diagnosed from soft tissue tumors based on the possibility of progressing to large lesions.
In conclusion, the present case highlights the importance of an early radical surgical approach to treat even cases with a small area of nevus.