Case 19 A woman with a skin lump on her leg

Martha was 35 years old when she consulted Dr Welch about contraception and also took the opportunity to mention a small lump on one of her calves. She mentioned the possibility of an insect bite on her lower leg which had occasionally been ‘weepy’ and had occasionally been scratched and bled. Dr Welch recorded ‘?pyogenic granuloma’. He recommended that Martha attend the practice’s Nurse Practitioner-run cryotherapy clinic.

Martha did this a couple of weeks later and the treatment appeared uneventful.

About a year later Martha presented with a lump in the groin. This proved to be due to metastatic amelanotic malignant melanoma, which was also confirmed in a small nodule at the site of the original cryotherapy. Unfortunately the disease was not treatable.

Before she died, Martha commenced a claim against Dr Welch.

Do you think a claim against Dr Welch will succeed?

Expert comment

Pyogenic granulomas are not common skin lesions. They tend to occur on the hand, lips, face or shoulder region. They are unusual on the lower leg.

Cryotherapy is a popular method of treating warts and other benign skin lesions. The difference, however, between cryotherapy and many other methods of treating skin lesions is that no tissue is available for histology. Therefore the diagnosis must be known with a high degree of certainty (which often is the case with skin tags, seborrhoeic keratoses and viral warts).

A pyogenic granuloma should not be treated with cryotherapy because, without histological confirmation, it may be an amelanotic malignant melanoma.

NICE guidelines suggest the use of a 7-point checklist with suspected malignant melanomas: looking for change in size, irregular shape, irregular colour, largest diameter 7 mm or more, inflammation, oozing, change in sensation. One problem is that the sensitivity of this clinical prediction rule is very low (around 40–50%) (Abbasi et al., 2004). A significant proportion of the pigmented lesions a general practitioner examines routinely should be referred urgently if the rule is strictly adhered to.

However, in this case the lesion was not pigmented. It was also on the lower leg in a woman. This is quite a common place for a malignant melanoma in women (the shoulders are commoner places for men). However, Dr Welch may quite reasonably not have even thought of the possibility that the nonpigmented lesion could be a malignant melanoma. Amelanotic melanomas are rare, and they are often described as ‘the great masquerader’ in skin lesions (Koch & Lange, 2000). Nevertheless, amelanotic melanomas are frequently misdiagnosed as pyogenic granulomas.

There are several potential criticisms of Dr Welch’s management which exemplify some of the types of cognitive error that may occur.

A probable source of error in this case was ‘premature anchoring’ bias – the tendency to begin from the assumption that a nonpigmented nodular skin lesion could not be a malignant melanoma. This form of cognitive error can be compounded by ‘confirmation bias’: the tendency to look for information that would be consistent with the preferred diagnosis, rather than information which would refute it. The lesion looks like the pictures of pyogenic granulomas in dermatology texts.

However, in this case the lesion was single, and it was on the calf. The site was therefore less usual for a pyogenic granuloma. A pyogenic granuloma has a differential diagnosis associated with it which includes amelanotic melanoma. It was necessary to ‘second guess’ the presumed diagnosis. Also, the information that the lesion had occasionally been weepy and bled was ignored.

Dr Welch had not recorded any history (duration, change in size or appearance) which would suggest that he had considered alternative diagnoses.

Realistically, it was a mistake to deal with the lesion by cryotherapy: any treatment method that gave tissue for histology would have been acceptable.

Legal comment

When the GP expert looks at Dr Welch’s very brief note (‘?pyogenic granuloma’) that will probably be enough for him to recommend that the case will be indefensible on breach of duty. Even if Dr Welch were to recall a number of reassuring circumstances to justify his decision to treat with cryotherapy, the fact he did not record them makes his position very weak indeed.

By contrast, Martha’s lawyers will take a detailed witness statement from her before she dies. It will describe the history of the lump and the consultation with Dr Welch. If she dies before the trial, that witness statement will stand as her evidence, even though it cannot be cross examined.

A dermatologist may conclude that earlier treatment of the melanoma would not have saved Martha’s life. But there was a delay of a year before she received treatment and so it seems likely that such an expert will conclude that earlier treatment would have made a difference.

The circumstances are overwhelmingly against Dr Welch. His MDO will want to settle the case on the best possible terms. If Martha is married and has children who are now deprived of a mother the case will be potentially expensive: well over £100 000. If not, then its value is limited to compensation for her suffering before death and the cost of care that she will have needed as her condition deteriorated.

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