Comedones and epidermal cysts on the abdominal skin of a dog occurring after a laparotomy

Abstract

An 8-year-old neutered male shih tzu dog underwent laparotomy for cystolithectomy. Ten days later, multiple various-sized cystic nodules were observed on the suture line and surrounding abdominal skin, although the surgical incision had healed well. Microscopically, various-sized cysts lined with thin walls of stratified squamous epithelium in the dermis were dilated and filled with keratin. Adnexal differentiation from the wall was not seen. Thus, the abdominal lesions were diagnosed as comedones and epidermal cysts. Herein, we describe the case of a dog with comedones and epidermal cysts on the abdominal skin after a laparotomy.

Key clinical message:

Multiple various-sized cystic lesions of the follicles are described. The implantation of epidermal fragments into the dermis by surgery may induce epidermal cysts and comedones in the skin of hyperadrenocorticism-affected dogs.

A comedo is a disorder of follicular keratinization characterized by cystically dilated, keratin-filled hair follicles (1). It consists of a small cystic cavity lined by a thin, stretched follicular infundibulum; the epidermis is variably acanthotic. Comedones occur when proliferation of keratinocytes blocks sebaceous secretions in the pilosebaceous ducts (2). The etiology of comedo formation is not clearly established; however, multiple possible etiologies and contributing factors have been suggested (2,3). In dogs, comedones of a genetic or congenital origin, such as the schnauzer comedo syndrome, as well as actinic and glucocorticoid-induced comedones, are well-described (1,4). Schnauzer comedo syndrome occurs only in miniature schnauzers and most likely represents a heritable, developmental follicular disorder of cornification (1,4). Actinic comedones occur in conjunction with chronic solar dermatitis, actinic keratoses, and other solar skin lesions, and the lesions are restricted to the sun-exposed regions, which are often non-pigmented or sparsely haired (1). Hyperadrenocorticism, or the injudicious use of topical glucocorticoids, is also a common cause of comedones, producing multiple milia-like lesions in dogs. Comedones associated with glucocorticoids are characterized by follicular keratosis with a thin epidermal and follicular epithelium and atrophic sebaceous glands (1). Follicular hyperkeratosis by demodicosis is also known to cause comedones, especially in German shepherds (1). Multiple epidermal cysts (also known as infundibular cysts, epidermal inclusion cysts, or epidermoid cysts) have been considered to originate from an expansion of comedones, and have been suspected to be a consequence of trauma; thus, local injury or trauma can be considered a cause of comedones (5–8). External trauma inducing the plugging or narrowing of the follicular ostia can cause a retention of follicular contents, dilation of the infundibulum of the occluded hair follicles, and eventually, the formation of comedones and follicular infundibular cysts (4,7,9). Thus, various factors contribute to comedo development. This case report describes the occurrence of comedones and epidermal cysts on the suture line and surrounding abdominal skin of a dog after it underwent laparotomy.

Case description

An 8-year-old neutered male shih tzu dog was brought to a local veterinary clinic with hematuria. After being diagnosed with nephrolithiasis and cystolithiasis, the dog underwent cystolithectomy by laparotomy, for which an incision was made from the umbilicus to the pubis. Antibiotics (cephalexin, 10 mg/kg, q12h) were prescribed for recovery. Ten days after surgery, when the dog was returned for suture removal, the incision had healed well. However, there were multiple various-sized cystic lesions on the suture line and the surrounding abdominal skin. Prednisolone (PDS) (Yuhan, Seoul, ROK), 0.3 mg/kg, q12h was prescribed for 2 wk, together with cephalexin, 10 mg/kg, q12h; and 2% chlorohexidine was used to disinfect the lesions topically. There was no noticeable improvement except for reduction of redness around the suture area. Furthermore, the skin had thinned rapidly during the treatment (Figure 1). However, clinical signs associated with hyperadrenocorticism, such as polyuria and polydipsia, were not present. Tissue samples were collected from the affected area and sent to the veterinary pathology laboratory for histopathological examination. The samples were fixed in 10% neutral-buffered formalin, processed routinely, and embedded in paraffin wax. They were sectioned at 4 μm, stained with hematoxylin and eosin, and examined microscopically.

Figure 1.

Gross examination of the dog’s skin. A — Multiple various-sized nodules are visible around the suture line (dashed line) 10 d after the laparotomy. The skin is dramatically thinned, as evidenced by prominent vasculature. B — Close-up view of multiple cystic lesions along the suture line, showing their varying sizes and numbers. There are numerous miliary blackheads and large nodular whiteheads.

Histological examination revealed various-sized cysts lined by thin walls of stratified squamous epithelium, with a granular cell layer resembling normal cutaneous epithelium in the dermis (Figure 2 A). The walls of the cysts were abruptly keratinized, including keratohyalin granules, and there were no adnexal structures radiating from the walls (Figure 2 B). Some cysts had pores connected to the overlying epidermis (Figure 2 C). The cysts were filled with laminated keratinous material and amorphous keratin flakes. Hair fragments were occasionally present in the larger cysts (Figure 2 D). All cysts had a similar histological morphology.

Figure 2.

Histological examination of the nodules in this dog. A — Various-sized cystic cavities lined by thin walls of stratified squamous epithelium. B — The wall of the cyst is composed of a thin layer of stratified squamous epithelium and a distinct granular cell layer with keratohyalin granules (arrow). There are no adnexal structures associated with the wall. C — A pore connects one of the cysts to the skin surface (arrow). D — Hair fragments (arrows) are present in the lumen of a cystic follicle, which is filled with laminated keratin and amorphous keratin flakes. Hematoxylin and eosin stain, scale bars: 100 μm (A–D).

In discussing the diagnosis with the veterinarian in charge of the dog’s surgery, it was revealed that, 5 mo before the surgery, the dog had developed iatrogenic hyperadrenocorticism caused by long-term PDS use for the relief of intervertebral disk disease pain. Thereafter, PDS administration was stopped during the 5-month period between the diagnosis of iatrogenic hyperadrenocorticism and the laparotomy. Although the adrenocorticotropic hormone stimulation test was not done at the time of surgery and the surgical incision healed well, iatrogenic hyperadrenocorticism was possibly still affecting the dog, as the abdominal skin had rapidly thinned from PDS administration for 2 wk after the cystic nodules were observed. Skin thinning is a characteristic of hyperadrenocorticism (1). Thus, based on the histological features and the dog’s history, the lesions were diagnosed as comedones and epidermal cysts related to hyperadrenocorticism and surgical traumatic irritation or implantation.

Discussion

Comedones and epidermal cysts occur because of blockage of the follicular orifice by mechanical injury, sun damage, or inactive hair follicles in some breeds, or in dogs with atrophic dermatosis related to hyperadrenocorticism (1,4,7,9). Multiple epidermal cysts are considered to be an expansion of comedones (5,6), and they differ from comedones (multiple milia) by their larger size (0.5 to 5 cm in diameter) (10,11). Sometimes, comedones are differentiated from epidermal cysts by the presence of sebaceous acini and a piliary unit; however, if comedones persist, the sebaceous glands and hair follicles also commonly atrophy, as occurs with epidermal cysts (10,12). Moreover, these sebaceous glands are also moderately to severely atrophic in glucocorticoid-induced comedones of dogs (1). In veterinary medicine, comedones and epidermal cysts tend to be classified according to their causes: genetic, actinic, or glucocorticoid-induced comedones; congenital, idiopathic, or trauma-induced multiple epidermal cysts (1,11,13,14). This may mean that the sizes of the expanded follicles differ depending on the cause. In the case herein, there were multiple various-sized cystic lesions on the abdominal skin, and the lesions varied from miliary blackheads to large, nodular whiteheads. Although the surgical incision had healed well, the dog seemed to remain under the influence of iatrogenic hyperadrenocorticism. Therefore, we suggest that surgical traumatic irritation, or implantation of epidermal fragments into the dermis by a laparotomy, may easily and rapidly cause epidermal cyst formation with comedones in the glucocorticoid-affected skin of a dog.

Comedones and epidermal cysts are not resolved without surgical removal. Although oral isotretinoin has been suggested for treatment, long-term administration is required, and the side effects from long-term use should be considered (7,15). Comedones, or multiple epidermal cysts, affecting a large area of the skin are difficult to remove entirely by surgical excision. Moreover, they may evolve into squamous cell carcinomas by enlargement and persistent ulceration of cystic lesions (16). Therefore, we suggest it is important to note that comedones or epidermal cysts may occur after surgery in dogs with hyperadrenocorticism. CVJ