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A practical approach to the skin case

How to reach a diagnosis earlier and avoid the frustrating dermatology case in small animal practice

19 October 2018, at 10:16am

Skin cases are very common in small animal practice and although many are straightforward, others do not respond to treatment and become chronic cases, usually without a definitive diagnosis. This account of a practical approach to the skin case aims to help first opinion practitioners avoid the frustrating skin case and achieve a diagnosis on most occasions. The complete approach to the diagnosis of skin cases can be summarised as follows:

  • Obtain a general and dermatological history
  • Perform a physical and dermatological examination
  • List and rank, in order of most likely to least likely, differential diagnoses
  • Make a diagnostic and therapeutic plan
  • Perform initial patient-side tests in virtually all cases and others as suggested by the ranked differential diagnosis list
  • Establish a diagnosis
  • Institute specific therapy

Allowing adequate time to obtain a comprehensive history is crucially important, especially with the apparently difficult case. Within the time constraints of a 10- to 15-minute consultation, it will not be possible to achieve a useful history in the more difficult case. There are several ways to overcome this problem.

Utilise the veterinary nursing team

Given that skin cases are so common, extra training of a nurse, or several nurses, in dermatology will be valuable. A dermatology nurse could take the history, perhaps with the aid of a set protocol, but emphasising listening skills. This information can then be given to the veterinary clinician at the initial consultation. Extra training of the veterinary nurse in patient-side diagnostic tests, which are invariably necessary in the dermatology case, will also be valuable. Thus, the veterinarian’s time is concentrated on the initial examination and compilation of the differential diagnosis list and the selection of those tests that are initially required.

Increase consultation length

An alternative is to allow at least half an hour for the history in any difficult case, and an hour on any case seen as a second opinion (which will usually have had a number of unsuccessful treatments). The involvement of the trained dermatology nurse is still recommended for the diagnostic tests required; the nurse would ideally be present at the consultation to establish a relationship with the owner.

This initial contact will be very useful; a trained dermatology nurse will also be the contact with the owner subsequently, to answer questions, be involved in follow-up consultations and help solve any compliance problems. If the practice already has a parasite control clinic run by nurses, it makes sense to add dermatology cases.

The time suggested above for taking a history is always well spent and appreciated by most owners. They should be advised that the initial consultation might take up to an hour, with the additional involvement of nursing staff. A thorough history may not need repeating in subsequent consultations, unless there is poor progress. In these cases, it is usually better to go back over the history to make sure nothing has been missed, rather than change treatment. If possible, avoid consultations by different colleagues. It is preferable to have one clinician in charge, ideally assisted by a nurse member of the team. This allows for better communication and a structured problem-solving approach.

Although a written protocol is helpful, a tick box approach does have limitations. Face-to-face consultations with an emphasis on listening is equally important.

Take a detailed history

Galen in the first century AD said: “Listen to your patient – he is giving you the diagnosis.” Many physicians have quoted this statement over the centuries and it is just as true now as it was nearly 2,000 years ago.

It is useful to be clear about the objectives in history taking. Ideally, they are to get the owner to describe the onset of the condition and its subsequent progress so that a diagnosis can be suggested.

Although there may be obvious lesions, there will usually be underlying causes that will only be suggested by a thorough history, with appropriate targeted questioning. Initially, many owners want to set their own agenda, concentrating on the problem as they see it. By allowing adequate time, the consultation can proceed in a structured way so that nothing is left out.

General medical history

A medical history before the dermatological history is important. Its objective is simply to establish whether the patient is well or unwell. If unwell, investigations to find the cause will be prioritised. There are also some conditions, such as hypothyroidism or hyperadrenocorticism, that have systemic signs and will be an underlying cause of the skin problem. Other problems, such as cardiac murmurs, need to be identified as subsequent dermatological treatment may cause deterioration.

In a general medical history, questions enquire about the diet and each body system, with abnormal signs such as coughing, sneezing, polydipsia, exercise tolerance, poor or excessive appetite and gastrointestinal signs evaluated.

Dermatological history

The objective is to encourage the owner to describe the initial lesions and what has happened since then. As implied above, it is essential to take charge and try to avoid the owner rambling – which is not always easy. A working knowledge of how dermatological diseases usually behave is important and can obviously be acquired, if necessary, by further study. Making sense of the information from the history, by asking the right questions and interpreting the answers, will be much easier with some additional knowledge.

Ask when the problem started. Young animals are more likely to suffer from parasitic diseases. Atopy usually begins in dogs between one and three years of age and is unlikely before six months or after seven years. Endocrine disease tends to occur from middle age onwards while neoplastic diseases are most frequently seen in old age.

Many conditions are pruritic. But when did this start? Can the owner remember whether the pruritus was prominent from the beginning or was the result of subsequent lesions? Secondary pyoderma will often cause a non-pruritic underlying cause to become pruritic.

It is very useful to assign a pruritus score. A simple method is to suggest that the non-pruritic animal is 0/10 and one that is constantly scratching (at night and in the consulting room), likely with prominent lesions, is 10/10. Where does your patient fit between these two extremes? Uncomplicated atopic dogs are often given a score of 4 or 5/10, for example. The pruritus score is useful because it will help with the differential diagnosis, and because the same question can be asked at subsequent consultations, suggesting deterioration or improvement (even if the owner does not perceive improvement at the time of the repeat consultation).

Is there evidence of contagion both to the owner and/or to other animals? Owners are sometimes reluctant to consider lesions on themselves but one of the advantages of adequate time is that, once relaxed, many will reconsider imparting this confidential information. Contagion from other animals is possible and more likely in those with an outdoor lifestyle. Enquiries can be made about grooming parlours, visits to shows and contact with foxes and, in the case of hunting cats, wild rodents.

Response to treatment

Unfortunately, it is not uncommon for some cases to defy a diagnosis. Many will have had multiple treatments with the involvement of several practices. Referral to a dermatology specialist would be ideal, but this is not always possible. The history in these cases, with a committed owner whose memory is good, can be very satisfying to unravel, and there are two objectives.

First, getting a description of the initial problem and how it evolved, as in the less complicated case. This will suggest in many instances a possible diagnosis.

Second, and an obvious complicating factor, is the assessment of the effect of prior treatment. Investigating this is much more time-consuming and is the reason for the longer consultation time that is always required in second opinion cases.

Some common questions include:

Have antibacterial agents been used?

Were appropriate agents with effectiveness against Staphylococcus pseudintermedius prescribed? Were they used at the correct dose and for an appropriate time?

If improvement was noticed, with subsequent relapse once the treatment was finished, the history is suggesting a diagnosis of pyoderma with an undiagnosed underlying cause. Inadequate treatment is often detected at this time due to one or more problems associated with antibacterial therapy.

Have glucocorticoids been prescribed?

What was the response? If good initially, it may suggest an allergic condition. Failure to respond, or frequent relapse increasing in severity once glucocorticoids cease, is often seen with secondary superficial pyoderma.

Have antiparasitic products been prescribed?

It is important to get the owner to describe how these were used, and whether there were any difficulties. Poor compliance is a major factor in all treatments, not just with antiparasitic drugs, and a careful evaluation is advised, particularly when pruritus escalates and becomes unresponsive to treatment with glucocorticoids. This is a common finding in an untreated scabies case.

If doubt exists on compliance, involvement of the nursing team is very useful in applying treatments or showing owners how to do it, then setting up follow-up appointments in a nurse clinic. In some cases, getting the treatment right is all that is required, even in the seemingly complicated case.

A methodical physical examination, involving all systems, is followed by a nose to tail examination of the skin. From the above, a ranked differential diagnosis list is formulated, suggesting appropriate patient-side diagnostic tests.

The British Veterinary Dermatology Study Group and The European Society of Veterinary Dermatology both host regular conferences and courses for all levels of knowledge. For information, visit: bvdsg.org.uk and esvd.org

David Grant, MBE, BVetMed, CertSAD, FRCVS, graduated from the RVC in 1968 and received his FRCVS in 1978. David was hospital director at RSPCA Harmsworth for 25 years and now writes and lectures internationally, mainly in dermatology.

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