Eccrine spiradenoma (ES) is a rare benign dermal tumor of apocrine differentiation originating from cutaneous sweat glands that may be sporadic or familial; it was first described in 1956 by Kersting and Helwing. It mainly affects adults, with the highest incidence in the fourth decade of life1. Yoshida et al.2 divided ES into solitary and multiple ES on the basis of its clinical appearance. Most presentations of ES are solitary and show no predilection for any sex. However, multiple ES predominantly affects women, with a male/female ratio of 1:3. Multiple ES can be described as multifocal or localized with a linear zosteriform distributionand nevoid or blaschkoid pattern (Table 1); however, there is no definitive classification3.

A 32-year-old Chinese woman presented to our hospital complaining of slow-growing painless itchy lesions on the left side of the back and forearm starting approximately 20 years ago with onset about 12-year-old previously as multiple nodules on the arm that gradually increased in size and number. When she was 12 years old, she received a hepatitis B vaccine injection on the left forearm. She stated her lesions were itchy but not painful, and that the itchiness increased after perspiration or eating spicy food. She also felt formication on occasion. She was otherwise well with no other significant medical or family history. Physical examination revealed multiple asymptomatic well-circumscribed blue-to-violet round-to-oval subcutaneous nodules; they exhibited a zosteriform distribution from the left upper back to the forearm (Fig. 1). On palpation, the lesions were rubbery, firm, and fixed to the overlying skin, ranging between 0.5 and 1.5 cm in size.

Histological analysis revealed 2 kinds of tumor cells: small darkly staining basaloid cells, and large pale cells. The nodules comprised basaloid cells arranged in a trabecular pattern surrounded by eosinophilic fibrous strands (Fig. 2). Small darkly staining basaloid cells and larger cells with pale nuclei in the center of the clusters and numerous scattered lymphocytes were observed, consistent with a diagnosis of ES. There was no evidence of malignant transformation.

Eccrine sweat glands are simple tubular glands that open directly to the surface; they are found all over the body, especially in the palms, soles, and axillae4. No cases of ES have been reported on glabrous skin or strong occurrence on the trunk, and head and neck regions. ES presents as a dermal or subcutaneous papulonodules of varying size up to 6 cm.It may mimic other painful skin tumors including leiomyoma, angiolipomas, neuroma granular cell tumors, etc.45. As such, computed tomography and magnetic resonance imaging can aid the diagnosis of this kind of tumor, especially for tumors in the deep dermis or subcutaneous tissues67. However, the definitive diagnosis of ES requires skin biopsy.

The etiology of ES remains unknown. Although autosomal dominant transmission has been suggested, this has not been confirmed2. ES has traditionally been designated a tumor of eccrine lineage thought to be an undifferentiated or poorly differentiated benign adnexal neoplasm8. The proposed mechanism of multifocal ES is that an abnormal clone of multipotent stem cells of the folliculosebaceous-apocrine unit arises during embryogenesis, subsequently producing a proliferation of abnormal cells and resulting in nodule formation and possible malignant transformation910. Trauma is proposed to be aprecipitating factor411, but the mechanism remains unsubstantiated. Although the present patient had a history of an injection, it is uncertain if this is coincidental or causative. Most cases of ES are solitary nodules, and multiple ES is rare: only 22 cases of multifocal segmental ES have been reported. ES exhibits no specific characteristic location, but the literature shows that most tumors are distributed on the front of the body and above the waistline (Table 1). The tumors 0.1~6.0 cm, and the age of onset ranges from 0~61 years. The most significant clinical characteristic of the nodules is pain or tenderness in 91% of patients, which occurred intermittently and was never continuous12; however, Mambo13 reports that pain and tenderness are less common. The cause of pain in ES is unclear. Moreover, the reasons for the various presentations of ES are unclear. The present patient exhibited multiple itchy ES nodules arranged in a zosteriform pattern; however, she had no family history of the disease.

Although most reported cases of ES are benign, long-standing benign ES can transform into malignant ES. Malignant transformation of ES is associated with aggressive behavior, a high recurrence rate, and the subsequent development of fatal metastases14. Although cases of benign ES with epidermal ulceration have been reported13, epidermal ulceration is still a clinical characteristic associated with carcinoma. De novo malignant ES has also been reported. Malignant transformation occurs more often in multifocal ES than solitary ES1.

Surgical excision is the predominant choice of treatment for tumor clearance; surgery is unnecessary if the lesions are not disfiguring, increasing in size and number, or painful. There are no clear recommendations for margins for standard excision1. However, if the tumors are multifocal or extensive, surgery is impractical; in such cases, radiotherapy or CO₂ laser should be considered as alternative treatments15. Ter Poorten et al.16 treated cases with small discrete lesions by surgical resection combined with CO₂ laser ablation; the treatment was effective with symptomatic relief. Trials using intralesional botulinum toxin A and intralesional triamcinolone have been used to treat multiple ES17. Nevertheless, additional long-term follow-up is required to determine the optimal management strategy.

ES is a benign tumor of unclear etiology originating from the eccrine sweat glands. It may present as multifocal tumors arranged in zosteriform pattern. Pain is usually the most striking symptom, but our patient only reported itching, especially after perspiration or eating spicy food; this is probably because ES originates from eccrine sweat glands, which would be most active in ES during perspiration16. Surgical excision is the mainstay treatment. Nonetheless, better methods are requiredto treat this disease.