Ep.42 - The 2p Piece Sized Problem: Acute Moist Dermatitis Explained (feat. Rosanna Marsella)
The Skin Flint PodcastShow Notes
CHAPTER 1 – Rosanna’s 2 Pennies Worth This month, Sue, John and Paul welcome Rosanna Marsella to the platform - Diplomate of the American College of Veterinary Dermatology and Professor at the University of Florida. 03:57 – John invites Rosanna to introduce herself. Thirty years as a veterinary dermatologist at the University of Florida, teaching, researching and treating small-animal allergy alongside some large-animal work; Florida's climate means plenty of infections. 04:42 – John asks how she'd categorise pyoderma. Rosanna explains it's classified by depth: surface pyoderma (often the "hot spot"), superficial pyoderma (essentially bacterial folliculitis), and deep pyoderma, where infection breaches the follicle wall into the dermis (furunculosis). 05:35 – Sue asks how dysbiosis differs from surface pyoderma. Allergic dogs already have reduced microbiome diversity, which shifts sharply toward Staphylococcus during a flare; dysbiosis is that pre-pustular shift, while surface pyoderma is the acute inflammatory skin-barrier damage that follows. 07:45 – Sue asks what AMD looks like clinically. Rosanna describes the classic picture: thick-coated dogs developing intensely pruritic, erosive lesions almost overnight on the face, rump or hips, driven by an acute trigger plus moisture trapped against the skin. 09:01 – John asks how important it is to find the trigger rather than just treat the lesion. Miss it, Rosanna says, and the dog either won't fully respond or will relapse. 09:54 – John runs through the usual suspects - fleas, allergic skin disease, ear disease, trapped moisture, pain, boredom. Rosanna splits these into predisposing factors (thick coat, heat, humidity, swimming) and primary triggers, ranking fleas top: an oral flea product still needs the flea to bite before it works, so a flea-allergic dog may also need a repellent. 13:37 – Sue asks whether lesion distribution helps distinguish flea-driven AMD from other allergies. Rosanna's rule of thumb: the back half of the body is fleas until proven otherwise; facial lesions warrant a work-up for pollen allergy or Malassezia otitis, both intensely itchy in their own right. 17:07 – John asks Sue whether "fleas first" holds in the UK climate too. Sue agrees fleas should be ruled out in every case, even with fast-acting isoxazoline parasiticides on board. CHAPTER 2 – More Than Skin Deep
18:30 – John asks what else sits on the differential list. Rosanna adds food allergy, pollen allergy and mite infestations including scabies, noting that food allergy - once considered rare in her caseload - now seems far more common and has moved up her checklist. 23:03 – Sue asks what diagnostics she'd reach for to rule out mimics such as mast cell tumours or diffuse neoplasia. Cytology is quick and informative, and she'll skip a deep skin scrape if the dog's already on a reliable flea/mite product. Older dogs with cutaneous lymphoma (mycosis fungoides) can present with hot spots as just one sign - something she sees fairly often in Florida's chronic atopic dogs. 25:59 – Sue asks how to tell surface from deep pyoderma. Largely a clinical call, Rosanna says: clip and check the edges for papules (superficial) versus draining tracts, nodules and infiltrated tissue (deep) - surface cytology can under-represent a deep infection, since it only samples the tip of the iceberg. 28:19 – John asks what the treatment priorities are once AMD is confirmed. Stop the itch and self-trauma first: clean the lesion, add an antimicrobial, and control inflammation with a steroid or JAK inhibitor while working out the cause - both act at a similar speed. CHAPTER 3 - No Quick Fixes
30:58 – John asks about physical barriers such as buster collars. Rosanna avoids them, preferring gabapentin to settle the dog and keep it off the area, given the known overlap between itch and pain. 31:59 – John asks when she'd reach for systemic antibiotics. Only for confirmed deep infection after an exam and cytology, w
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