DR. KEITH LINDER DVM, PhD, DIP. ACVP NORTH CAROLINA STATE UNIVERSITY COLLEGE OF VETERINARY MEDICINE
This lecture followed Petra Bizikova’s two lectures on autoimmune diseases. All three lectures are well worth watching as a unit and several times as they bring together a huge amount of useful information.
Keith began his presentation by outlining the pros and cons of dermatohistopathology. Pros include a rapid diagnosis of many diseases while allowing differentiation of multiple conditions. Against this the cons could include that the procedure is costly, invasive and misapplication is easy. This can be misleading and result in diagnostic delay. To maximise benefit an approach was suggested.
- Select appropriate patient
- Identify all skin lesion types present
- Prioritise lesions as primary or secondary
- Select biopsy site where there are primary lesions
- Choose biopsy method and number of samples
Primary lesion examples are papules, nodules, pustules, plaques, tumours, vesicles, bullae and atrophy that is not part of a scar
Secondary lesions are excoriations, scar tissue, lichenification, callus and hyperpigmentation
Some lesions may be primary or secondary, for example alopecia following self-trauma, erosions and depigmentation. The history and physical examination should help with the differentiation.
The main biopsy techniques used in veterinary medicine are:
Punch biopsy (take 6-8 biopsies) Punch biopsy is the commonest method
Shave biopsy (take 1-3 biopsies)
Wedge biopsy (take 1-3 biopsies)
Keith advises ‘throwing away’ any biopsy punch less than 8 mm and favours the 8mm. He still gets biopsies from quite severe skin conditions using 4mm punches-not a lot of material to work with.
Following the introduction he introduced the first case
This was a case of Fleabite Hypersensitivity in a dog. Lesions shown were lichenification, hyperpigmentation, macules and patches of erythema and alopecia. Just as with Petra Bizikova’s presentations Keith had thought about his audience assuming there would be some new to dermatology. Any dermatological term like patch or macule was clearly defined and illustrated.
The conclusion from this case was that histopathological examination would not be helpful as all the lesions were secondary. The report would be eosinophilic hyperplastic perivascular dermatitis. The differentials would be the same as those suggested by clinical examination.
Following this a basic point was that in general biopsies from primary pruritic patients are not likely to be diagnostically useful. Biopsy from patients where pruritus is a secondary feature may be more useful and in those cases where the pruritus is not explained by allergy, ectoparasites or self-trauma. An epitheliotropic lymphoma case in a dog was shown where pruritus was evident. This dog had generalised erythema, scaling, papules, plaques and nodules. Other less useful scenarios for biopsy include most cases of endocrine alopecia. It is best to treat pyoderma first prior to biopsy and for the animal to be off steroids for at least 3 weeks prior to biopsy. Active primary lesions are most likely to yield diagnostic information
The rest of this presentation featured cases of Eosinophilic folliculitis and furunculosis in a dog, Eosinophilic plaque in a cat, Feline herpes virus ulcerative dermatitis, Bullous pemphigoid in a dog, Discoid lupus erythematosus in a dog, Vaccine induced ischaemic dermatopathy in a dog and finally a cat with panniculitis.
In each case lesions were described, active primary lesions were demonstrated and a diagnosis was made. With each case the best type of biopsy (punch, shave, or wedge) was suggested along with the best site from which to take the sample and how to do it to maximise the possibility of an accurate diagnosis
This veterinary webinar was excellent, not only for the extremely logical way in which the diagnostic approach and biopsy sites were described, but also for the high quality clinical pictures. Case presentations from pathologists are always fascinating and attention doesn’t waver, and this is even better when it is a double act from a clinician and pathologist. The webinar by Keith Linder and the preceding two on autoimmune diseases by his wife Petra Bizikova are a must see whether you are established in dermatology, starting out or just want to do things well. Do not be surprised if you become hooked!