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Latest update 16/06/09
Definition
- A giant comedone is an exceptionally large blackhead
Key diagnostic features
- Usually single but occasionally several can be found
- People who have very bad acne and atrophic scars are much more prone to developing giant comedo, however they frequently occur in the absence of previous acne
- Age - occur more in the middle-aged and elderly age groups
- Distribution - many parts of the body but especially on areas which are rich in sebaceous glands such as the face, back and chest and occasionally where there are apocrine glands, as in the axillae, groins, perianal areas and scrotum
- Size - lesions are frequently of the order of 2-3 mm but can be up to 1cm
Histology
- A distended upper part of either the pilosebaceous duct of the sebaceous gland or the duct of the apocrine gland. It is suggested that the decrease in dermal collagen with age, sunlight or both facilitate the easier distension of the follicular duct once the process is underway. Once initiated the problem is a vicious cycle
- The abnormalities that arise could be due to either an increased production of the corneocytes lining the duct and, or an associated decrease in the rate at which the ductal corneocytes separate - but there is no data to confirm either of these suggestions
Treatment
- The diagnosis is usually straightforward as it is normally very easy to squeeze out the contents of the very distended duct. This is best done by placing a little piece of gauze either side of the thumb and pressing gently
- The problem is that in most instances the follicular ducts refill over a period of two to three months. Cautery of the residual duct, having evacuated the contents does not seem a very successful procedure. If the comedo is problematic it may be worth a trial of topical retinoids but no study has ever looked at this treatment
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Figure 1 – Gaint comedone left cheek
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Figure 2 – Close up of figure 1
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Figure 3 – Close up of giant comedone behind ear
Gentle pressure would allow expression of the contents through the punctum (black arrow)
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Figure 4 – Close up of giant comedone
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