Imagine you are a final year medical student – you’ve completed most of your rotations in surgery and in medical specialities. Your final one before graduation is dermatology and you are just about to enter an outpatient clinic. You have seen third degree burns, all the rash patterns are ingrained in your mind and you can rattle off the clotting cascade from memory. The consultant gathers you and your fellow medical students to take a look at a patient. She has quite a distinctive fringe but nothing seems too off about her skin. And then you notice it – under the fringe, something is protruding. It is not a blister nor is it swelling. It is a horn.
This defect is known as a ‘cutaneous horn’, owing to its origins from our skin. Suffice to say, they are not common and when they do present, they are certain to pique interest. From this week onwards , I’ll attempt to cover various aspects of clinical medicine and take you through their importance but also how fascinating they can be.
Back to the horn. For the consultant, a consultation will always begin with the sharpest tool in the medical toolkit – questions. However, taking a medical history is a topic for another time. This is because although questions are an indispensable tool, cutaneous horns are usually asymptomatic. This also shapes treatement towards it – although it is the cutaneous horn that looks the most alarming, very rarely is it the problem. Normally there are much more subtle devious works at play, which require their corresponding treatment. Very little can be done without a biopsy of the horn as to get an idea of what you are dealing with, you need to dig deeper right down to the cellular level.
Cutaneous horns can present with a plethora of underlying pathologies – 60% of these are benign but there is always the darker, uglier possibility of malignancy. The benign causes of the horn are thought to include viral diseases caused by human papillomaviruses. This family of viruses is best known for their role in cervical cancer. However, their structure mean they are well equipped to deal damage to other kinds of epithelial tissue, and in this case, the skin.
They enter the skin through breaks in epithelial tissue and can survive for months. As A level biology students will know, the viral pathology of most viruses is through causing cells to burst (cytolysis). HPV is different in that the lesions that arise occur because of infected skin cells, which proliferate. This can then result in outward growth and therefore a horn.
The malignant nature of the other 40% of cases is thought to arise as a result of sun exposure and ultraviolet radiation, which is also well documented as a causative agent for other types of skin cancer. The UV radiation causes changes in cells with the hallmarks of cancer such as genomic instability and mutation, as well as initiating tumour-promoting inflammatory responses. This set of abnormal cellular behaviours characterise cancer and promote development and progression of tumours, such as those seen in cutaneous horns.
As an entry titled under clinical medicine, I will attempt to explain how such an affliction is managed. For a benign cutaneous horn, simply excising the horn will be sufficient. This is, as mentioned previously is carried out by dermatologists, and as procedures go, a pretty simple one.
Check this video out if you are interested:
Skin cancer treatment is also mainly surgical. This is because these are normally detected at an early stage when the spread is localised and not systemic – meaning the treatment options would reflect this too. Hence, surgery is the most common option. However, chemotherapy may also be used – normally on a smaller scale. Topical chemotherapy is local and as such less extreme than systemic chemotherapy – one example of this is fluorouracil. This acts by inhibiting the enzyme thymidylate synthase, which prevents synthesis of thymidine, which is needed for DNA replication. The ‘replicative immortality’ that is an hallmark of cancer is therefore dealt with.
Cutaneous horns – a fixed projection on the surface but a dynamic pathology underneath. Although the clinical management plans of these is among the more simple ones, there is no denying the utterly fascinating, utterly bizarre phenomenon of ‘a human unicorn’.
- Dr Tina Tian, Medical Oncology Registrar, Hawke’s Bay Hospital, Hastings, New Zealand https://dermnetnz.org/topics/cutaneous-horn/ 2013
- Moore, AY (2009). “Clinical applications for topical 5-fluorouracil in the treatment of dermatological disorders”. The Journal of Dermatological Treatment. 20 (6): 328–35.