Older Male with Red Nodule on Arm

Evan Farmer, M.D.

Specimen Type:



The patient is 84-year-old man with a red nodule of one year duration on the arm. He has no systemic symptoms or other abnormal physical findings related to this nodule. The biopsy was from the nodule.

Pathologic Features:

The specimen has proliferation of small, bland spindle-shaped cells throughout the reticular dermis sparing the adnexal structures and adipose tissue. No atypical cells or mitotic figures were seen. The overlying epidermis was normal for the anatomic site. No significant inflammatory infiltrate was present. The cells are positive for SMA and negative for S-100 protein.

Differential Diagnosis:

  • Fibromatosis
  • Dermatofibroma
  • Dermatofibrosarcoma protuberans
  • Dermatomyofibroma



Dermatomyofibroma is a rare, benign, dermal tumor of fibroblastic/myofibroblastic origin. It occurs most frequently on the shoulder and arm and tends to be in young adults, but has been reported in children. The primary differential is between a dermatofibroma and a dermatofibrosarcoma protuberans. The histologic features and immunoperoxidase staining help in this differentiation.


  1. Kamino H, Reddy VB, Gero M, Greco MA: Dermatomyofibroma. A benign cutaneous, plaque-like proliferation of fibroblasts and myofibroblasts in young adults. J Cutan Pathol. 1992 Apr;19(2):85-93.
  2. Mentzel T, Kutzner H: Dermatomyofibroma: clinicopathologic and immunohistochemical analysis of 56 cases and reappraisal of a rare and distinct cutaneous neoplasm. Am J Dermatopathol. 2009 Feb;31(1):44-9.