Dermatomyofibroma
(plaque-like dermal fibromatosis) represents a distinct clinicopathological entity in the spectrum of cutaneous mesenchymal
neoplasms showing a myofibroblastic line of differentiation.
Age:
Occurs mostly in adolescents and young adults. These benign neoplasms
occur frequently, but not exclusively, in young women.
Site: Shoulder girdle,
neck, axilla, upper arm and abdomen.
Gross: Firm red-brown
plaques or nodules 1- 2 cm in diameter. Keloid like and linear variants may occur.
| Microscopic
features:
Histologically, these are
non-encapsulated but well-circumscribed, plaque-like lesions located in
the reticular dermis.
The tumour is composed of
bland spindle-shaped tumour cells containing an ill-defined, pale
eosinophilic cytoplasm and elongated, neuroid nuclei.
Neoplastic cells are
arranged in bundles and fascicles orientated parallel to the skin surface.
The fascicles are
separated from the epidermis by a Grenz zone.
There is no evidence of
cytologic atypia and mitotic figures are infrequent.
The adnexal structures are
spared and elastic fibres are increased and fragmented.
The lesion may extend to
the upper part of the subcutaneous septa in some cases.
|
Immunohistochemistry:
Tumour
cells express vimentin and variably muscle actin and alpha-smooth muscle
actin, but are negative for desmin, CD34, S100, and epithelial
markers.
Some dermal dendrocytes stained positively for Factor XIIIa, but the
spindle-shaped cells were negative.
Electron microscopy
: Revealed a mixture of fibroblasts, myofibroblasts, and undifferentiated mesenchymal
cells.
| Differential
diagnosis:
- Dermatofibroma (fibrous
histiocytoma) ;
- Pilar leiomyoma
;
- Neurofibroma
;
- Adult myofibromatosis ;
- Extra-abdominal
fibromatosis ;
- Hypertrophic scar ;
- Plaque-stage
dermatofibrosarcoma protuberans.
(In dermatomyofibroma- Storiform
pattern is not present, pattern of infiltration is limited, Actin positive and CD34 negative)
;
- Plaque-stage Kaposi's
sarcoma- (abundant extravasated
erythrocytes, scattered inflammatory cells, numerous capillaries, and
sieve-and slit-like spaces may be present
in haemorrhagic
dermatomyofibroma. The spindled tumour cells are
negative for CD34, and HHV8).
|
All lesions are treated
by conservative excision.
|
