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A proliferating pimple

Q1: What is the differential diagnosis on clinical examination?
The possible differential diagnosis on clinical examination is:

• Dermatofibroma.
  
• Pyogenic granuloma.
  
• Malignant melanoma.
  
• Metastatic oat cell carcinoma.
  
• Angiosarcoma.
  

Q2: What does the histology reveal (see p 249) and what histological techniques are used to establish the diagnosis?
The histology reveals malignant round cells consistent with a Merkel cell carcinoma or trabecular carcinoma. This is a rare primary cutaneous neuroendocrine tumour arising from Merkel cells.

History
The Merkel cell is a round cell in the basal layer of the epidermis named after Fredrick Sigmund Merkel who discovered it in 1875. These round cells may be isolated or arranged in clusters around hair follicles, which are innervated and function as touch receptors. The tumour was first described by Toker in 1972 who, along with Tang in 1978, described the intracytoplasmic dense core granules similar to those seen in neuroendocrine cells.¹

Q3: Discuss the clinical features and management of this lesion
Clinical features
The Merkel cell carcinoma is a rare but aggressive tumour presenting as a dark red to dark blue papule. It usually arises on the head, neck, and the extremities of the elderly.² . . . [Full text of this article]

Relevant Article

An episodic eruption

P Bentley and A Keat
Postgrad. Med. J. 2002 78: 249. [Extract] [Full Text] [PDF]