Paraganglioma-like dermal melanocytic tumour, PDMT

Definition

A very rare benign dermal melanocytic lesion showing a packeted pattern. There is no implied lineage relationship to paraganglioma. This entity is based on a report of eight tumours. PDMT would have been previously categorised in the AFIP fascicle as "melanocytic tumor of uncertain malignant potential".

Epidemiology

PDMT is a lesion predominantly of adult females.

Clinical features

All lesions were located on the extremities, with no overlying pigmentation.

Histopathology

PDMT is usually a circumscribed nodular lesion of the dermis and subcutis. There is no overlying junctional component or epidermal hyperplasia. Sometimes the nodules are multiple of the lesion is infiltrating. Tumour cells are arranged in small and large packets separated by fine fibrous septa. There is fine dust-like melanin pigment. Some cases show clear cytoplasm. Atypia is limited and the mitotic count is low (0-4/10HPF). Necrosis is not seen. There may be a peritumoral lymphocytic infiltrate.

Immunohistochemistry

	S-100	8/81
	HMB-45	8/81
	Melan-A	4/81
	MITF	8/81
	AE1/AE3	0/81
	SMA	0/81

Ultrastructure

Cytogenetics

The t(12;22)(q13;q12) translocation typical of clear cell sarcoma is absent.

Differential diagnosis

• Neurocristic hamartomata: are highly pigmented and show infiltration of the dermis by pigmented dendritic and spindle cells. They include:

  • cellular blue naevus
    
  •  epithelioid naevus seen in Carney's syndrome
    
  • congenital naevus
    
  • dermal melanocytoma

• Clear cell sarcoma: this is a deeper lesion, centred on the fascia/tendons. Nucleoli are prominent and there are scattered tumour giant cells. There is a characteristic t(12;22)(q13;q12) translocation producing an EWS/ATF1 chimeric protein.

• Melanoma, metastatic or a dermal primary.

• Clear cell epithelial tumour: positive for cytokeratin.

• PEComa: positive for SMA

• Melanotic Schwannoma

Prognosis

On the limited experience, these lesions are benign after conservative complete excision.

References

¹Deyrup, A. T., P. Althof, et al. (2004). "Paraganglioma-like dermal melanocytic tumor: a unique entity distinct from cellular blue nevus, clear cell sarcoma, and cutaneous melanoma." Am J Surg Pathol 28(12): 1579-86.

This page last revised 4.1.2005.

©SMUHT/PW Bishop