Bullous pilomatricoma: a rare variant resembling bouncy ball.

Pilomatricoma (pilomatrixoma) or calcifying epithelioma of Malherbe, is a tumor with differentiation toward hair cells, particularly hair cortex cells. It frequently presents as a firm, deep-seated nodule that is covered by normal skin. Bullous pilomatricoma is an unusual clinical variant. Reports on bullous variant of pilomatricoma is sparse, and only 17 cases have been reported world-wide until date out of which only two cases are reported from India. We present a report of a 17-year-old female with a solitary reddish semi-transparent blister over her right upper arm since 3 months resembling a bouncy ball. Histopathology revealed tumor nests of basophilic cells and eosinophilic shadow cells, which are consistent with pilomatricoma.

INTRODUCTION

Pilomatricoma also known as benign calcifying epithelioma of Malherbe is an uncommon slow growing benign adnexal skin tumor, which differentiates towards the hair matrix. It is the commonest hair follicle tumor. Upto 75% of pilomatricomas possess activating mutations of the β-catenin gene.[1] Here, we report a case of pilomatricoma with bullous appearance in a young female which is rare, and also review the literature on bullous pilomatricoma.

CASE REPORT

A 17-year-old girl presented with a solitary reddish semi-transparent blister over her right upper arm since 3 months. Initially, the lesion started as a solid pin-head sized papule, which gradually progressed to form a semi-transparent blister with a hard nodule inside. No history of local trauma or insect bite. No history of similar lesions in the past or in family members.

On examination, single 2 cm sized erythematous semi-transparent bullae with a white nodule was seen on the medial aspect of the right upper arm [Figure 1a and b]. The appearance of this resembled a bouncy ball [Figure 2]. On palpation, the bullae had a jelly like consistency and the nodule underneath was hard. On puncturing the lesion, it oozed a jelly like material. Systemic examination was normal. We considered a differential diagnosis of infected sebaceous cyst and dermatofibroma.

Figure 1

(a and b) 2 cm sized erythematous semi-transparent bullae with a white nodule inside

Figure 2

Photograph of a bouncy ball

Routine investigations were normal and excision biopsy was carried out [Figure 3]. Histopathology revealed islands of basaloid cells with central abrupt keratinization and dilated lymphatics with dermal edema [Figures 4 and 5a]. Ghost cells (shadow cells) [Figure 5b], foreign body giant cell reaction [Figure 5c], and small foci of calcification were also seen [Figure 5d]. With these findings, diagnosis of bullous pilomatricoma was made.

Figure 3

Gross specimen of excised material

Figure 4

Histopathological features of excision biopsy showing islands of basaloid cells with central abrupt keratinization, shadow (ghost) cells, and dilated lymphatics with dermal edema (H and E, ×10)

Figure 5

(a) Basaloid cells undergoing abrupt keratinization; (b) Ghost cells/shadow cells; (c) Foreign body giant cell reaction; (d) Small foci of calcification (H and E, ×40)

DISCUSSION

Pilomatricoma is a benign tumor considered to be a hamartoma of the hair matrix composed of cells resembling those of the hair matrix, cortex, and inner root sheath. The cells usually undergo “mummification.” It makes up around 20% of all hair follicle-related tumors and is the commonest hair follicle tumor. Majority of patients are under 20 years of age, and females are affected more often than males. It is usually a solitary, deep dermal or subcutaneous tumor 3-30 mm in diameter situated on the head, neck or upper extremities.[2] Clinical variants include, large (giant),[3] extruding or perforating lesions, ulcerative lesions, multiple eruptive cases, familial cases, superficial pilomatricoma presenting as a cutaneous horn and bullous pilomatricoma.[4] Association with myotonic dystrophy,[5] Gardner's syndrome,[6] Turner's syndrome,[7] and Rubinstein Taybi syndrome[8] have been reported with pilomatricoma. However, no such associations with bullous pilomatricoma has been reported.[9]

Reports on bullous variant of pilomatricoma is sparse, and only 17 cases have been reported worldwide until date out of which only two cases are reported from India.[91011] Bullous pilomatricoma has a predilection for occurring on the shoulder and upper arm regions, predominantly in females. It can also be found on the neck, trunk, eyelid, and scalp. The peak age of presentation is 10-20 years, and mostly of sizes 1-3 cm. Usually presents as a solitary, flaccid, thick-walled red bullae with an underlying palpable hard nodule. Our present case is consistent with these reports. Since our case resembled a bouncy ball, we would like to coin this as the “bouncy ball” sign in bullous pilomatricoma. Histopathological hallmarks of pilomatricoma are the tumor nests of basophilic cells and eosinophilic shadow cells.[12] Bullous variant in addition to these findings, show dilated lymphatic vessels, giant cell reaction, lymphoedema, disruption of collagen fibers, dilated blood vessels, fibrous capsule, calcification, nests of transitional cells, and necrosis.[9] Our case is consistent with these findings which showed islands of basaloid cells with central abrupt keratinization, shadow cells, dilated lymphatics with dermal edema, foreign body giant cell reaction and small foci of calcification.

Different theories have been proposed for the mechanism of bullae formation in pilomatricoma. It could be due to mechanical irritation,[13] or it could be a pseudoblister[14] since the bullae-like spaces are filled with lymphatic fluid. Another theory, suggests that the tumor cells or infiltrating inflammatory cells produce elastinolytic enzymes which disrupt the collagen fibers and destruct and dilate the lymphatic vessels, which lead to accumulation of lymph fluid in the dermis causing a bullae.[1315] However, the widely accepted theory is that obstruction of lymphatic vessels and congestion of lymphatic fluid caused by the growth of tumor nodule causes dilatation of lymphatic vessels, leakage of lymphatic fluid, and edema in the dermis surrounding the tumor resulting in the bullous appearance.[915]

Malignant change (pilomatricarcinoma) is recorded in several cases, and appears to arise chiefly in large pilomatricomas that have been present for a long time.[2] However, malignant transformation has not been reported in the bullous variant.[9]

In conclusion, dermatologists should be aware of this rare variant of pilomatricoma and excision biopsy is the norm for diagnosis and treatment of this condition.