Skin conditions

Question 1

Factors that increase risk of SCC metastasising to lymph nodes (6)

Answer 1

> 2cm diameter
4mm thick
Poorly differentiated
Perineural invasion
Recurrent
Ears and lips

Question 2

Define carbuncle

Answer 2

A deep-seated infection of the soft tissue with multiple openings onto the skin via hair follicles

Question 3

Define SCC
What skin condition does it arise from?

Answer 3

A cancer of the superficial keratinised layer of the epidermis, above the basal layer
Actinic (solar) keratoses

Question 4

Appearances of SCC

Answer 4

Symmetrical
Keratinised centre
Ulcers or fungating lesions with heaped up edges

Question 5

Appearances of BCC

Answer 5

Slow-growing
Pearly nodule, waxy
Telangiectatic vessels on surface
Centre can die and the edges will appear rolled or elevated (not inverted)
Easily bleed and ulcerate

Question 6

Outline the pathophysiology of necrotising fasciitis

Answer 6

Facultative anaerobes lower the oxidation-reduction potential of microenvironment
Anaerobes multiply
Anaerobes interfere with phagocytes
Aerobes proliferate
Toxins: hyaluronidase, lipase, streptokinase, collagenase - aid tissue spread
Thrombosis of surrounding vessels

All leads to rapid spread of infection along fascial planes and breakdown of surrounding skin, muscle and other tissue

Question 7

What is Merkel cell carcinoma?

Answer 7

A malignant transformation of neuroendocrine or stem cells in the basal layer of the epidermis, due to infection with dsDNA polyomavirus causing clonal expansion of Merkel cells.

Risk factors include age >50, pale skin, chronic UV exposure, immunosuppression, haematological maligancies

Clinically rapidly expanding, painless nodule in UV-exposed skin

Histology: monotonous round basophilic cells, CK20+