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A missed diagnosis but no negligence

13 April 2018
By Dr Ellen Welch, GP

Ms M, 42 years old, presented recurrently to her GP with widespread pruritis over her entire body and scalp. A reasonable period of topical treatments in primary care failed to improve her symptoms and she was referred to a consultant dermatologist, Dr H.

Dr H reviewed Ms M on four occasions over the following six months. During each consultation, a specialist nurse was present who watched Dr H carry out a detailed full body examination on Ms M, using magnification with a dermatoscope to visualise her skin lesions. 

Dr H found no evidence of scabies infestation on examination, and reached a diagnosis of a prurigo-type eczema with a possible underlying contact dermatitis. Histopathological examination of Ms M’s skin biopsy also confirmed a diagnosis of nodular prurigo. She was prescribed a potent topical steroid and oral prednisolone, which produced some symptomatic improvement.

Unhappy with the lack of a complete resolution of her symptoms, Ms M sought a second dermatology opinion and was diagnosed with scabies following the identification of what appeared to be a burrow. She was given antiscabetic treatment, with no sustained response, and subsequently required further prednisolone, PUVA treatment and eventually dapsone to control her symptoms. Dapsone is a sulphonamide antibiotic, used to treat a variety of skin conditions unresponsive to first line therapy. It requires careful laboratory monitoring to avoid anaemia, and would not be used as a treatment for scabies.

Ms M made a claim against Dr H, complaining that she had failed to recognise that her symptoms were due to scabies, and that Dr H had failed to perform any diagnostic tests such as skin scrapings to establish the diagnosis. Ms M claimed that the failure to diagnose scabies caused her months of itching, scratching and pain before she received the correct treatment, and that the delay had led to the development of nodular prurigo, scarring, and severe psychological trauma.
 
Expert opinion
An expert dermatologist reviewed the case records and found that Dr H’s practice was in accordance with that of a responsible body of dermatologists. It was concluded that Dr H conducted a diligent search for the scabies mite using a dermatoscope, but that no lesions were present on which to base a diagnosis. 

The expert explained that the diagnosis of scabies is based on the visual appearance of the burrow track or of the parasite itself, and skin scrapings were not necessary. In his opinion, if burrows were not found after such a detailed examination, witnessed by a nurse, it was unlikely any scabies were present at that time. He remarked that the distribution of Ms M’s rash was also completely outside the normal pattern of scabies, as it involved the scalp and ears and the symptoms recurred after a transient response to antiscabetic medication – requiring further treatments and eventually dapsone for long term suppression.
 
Furthermore, the expert noted that Ms M’s partner had remained rash and symptom free throughout the two years Ms M had been suffering with these symptoms, and if she had indeed had scabies, then he would have expected her partner to have been also infected. He supported as reasonable Dr H’s diagnosis of severe widespread eczema complicated by nodular prurigo, which was confirmed on histological examination of a skin biopsy.

However, the expert went on to comment that Ms M’s widespread excoriations could have destroyed any evidence of scabies infestation, and that the potent topical steroids and oral steroids she was reasonably prescribed could have over time exacerbated an infestation of scabies, enabling the dermatologist who provided the second opinion to detect a scabetic lesion. 

In conclusion, it was considered that Ms M suffered from long-term severe eczema with, at times, seborrheic features and nodular prurigo verified by biopsy. There was suspicion but no proof that scabies may have been present at some point, and the clinical course of the condition was within the range of that expected in severe eczema. If scabies was present, it was mixed in with a severe to gross degree of eczema/dermatitis and nodular prurigo. 

The claim against Dr H was subsequently discontinued.

Learning points
  • Scabies is an itchy skin condition caused by Sarcoptes scabiei, a tiny burrowing mite. The word scabies comes from the Latin scabere, to scratch. One of the first symptoms is intense itching, especially at night. Management involves the application of topical antiscabetic treatment to all areas of the body for both the patient and household members and sexual contacts, together with decontamination of bedding, clothing and towels.

  • From a medicolegal perspective, there is no breach of duty if practice does not fall below a reasonable standard; it is thus possible to miss a diagnosis of scabies without negligence if, as in this case, a patient is examined thoroughly and carefully with a view to the possibility of scabies being present, but no diagnostic lesions are found.

  • In this particular case, there were a number of strong factual points that supported the absence of scabies at the time the Ms M attended Dr H, which once again highlights the importance of detailed medical record-keeping with every consultation. Having a chaperone present during examination also provides corroborative evidence of practice, should an issue be raised afterwards.