In skin histopathology, an increased density or number of eccrine ducts within the dermis is categorized as eccrine duct hyperplasia, a hamartomatous malformation, or an adnexal neoplasm. [1, 2, 3]
The primary conditions and reactive processes that present with an excess of eccrine ducts in the dermis are classified below by their underlying pathology:
Benign Adnexal Neoplasms and Tumours
- Syringoma: This is the most common benign adnexal tumour presenting with numerous small eccrine ducts in the upper dermis. Histologically, it displays characteristic "tadpole-like" structures or comma-shaped tails, lined by a double layer of cuboidal epithelium embedded in a dense sclerotic stroma. [1, 2, 3, 4, 5]
- Eccrine Syringofibroadenoma (ESFA): Characterised by hyperplastic, anastomosing cords and strands of monomorphous basaloid cuboidal epithelial cells extending from the epidermis into the dermis, interspersed with well-formed eccrine duct structures set in a fibrovascular stroma. [1, 2]
- Dermal Duct Tumour: A variant of poroma confined to the superficial dermis, showing small, solid, and cystic nodular aggregates of poroid and cuticular cells with prominent ductal differentiation. [1, 2, 3]
- Eccrine Mixed Tumour (Chondroid Syringoma): Displays small, non-branching eccrine ducts lined by a double layer of bland cells embedded in a highly characteristic fibromucinous, myxoid, or chondroid (cartilage-like) matrix. [1]
Reactive and Metoplastic Proliferations
- Reactive Eccrine Duct Hyperplasia: This is not a distinct clinical entity but a histological reaction pattern where normal eccrine ducts proliferate secondary to adjacent pathology. It is frequently found adjacent to, or overlying:
- Syringolymphoid Hyperplasia with Alopecia: A rare reactive condition marked by a dense lymphoid infiltrate surrounding an increased number of hyperplastic eccrine ducts, often leading to localized hair loss. [1, 2]
- Papular Clear Cell Hyperplasia of the Eccrine Duct (PCCH): Histologically presents with widened, hyperplastic eccrine ducts containing clear cells with optically empty cytoplasm due to glycogen deposition (frequently associated with diabetes). [1, 2]
Hamartomas and Nevi
- Eccrine Nevus / Sweat Gland Nevus: A rare, benign structural malformation present from birth that displays a localized, marked increase in the absolute number and size of normal-appearing eccrine coils and ducts within the dermis. [1]
- Mucinous Eccrine Nevus: A rare variant of an eccrine nevus showing an increased number of dermal eccrine ducts and coils embedded within an abundant, alcian-blue-positive acid mucosubstance. [, 2]
Malignant Adnexal Tumours (Adenocarcinomas)
- Ductal Eccrine Carcinoma / Adenocarcinoma: Features atypical epithelial cells with pleomorphic, hyperchromatic nuclei forming infiltrative niches, cords, and prominent tubular or ductal arrangements within a desmoplastic stroma. [1]
- Microcystic Adnexal Carcinoma (MAC): A deeply infiltrative, low-grade malignant tumour that displays numerous nests and small, duct-like structures embedded in a dense sclerotic stroma. It closely mimics benign syringomas superficially but tracks deeply into the subcutaneous tissue, muscle, and nerves (perineural invasion). [1, 2, 3, 4, 5]
