Tufts University School of Veterinary Medicine, Dermatology & Allergy Services, Walpole, MA, USA; Bizvet, Inc., Westborough, MA, USA
© 2005 Lowell Ackerman DVM DACVD MBA MPA [No part of this material may be reproduced or distributed without express written consent of author].
Sebaceous adenitis is a periappendageal inflammatory process directed against hair follicles and glands. It is presumed autosomal recessive in Standard poodles but the condition in other breeds may be quite different. An immune-mediated process is suspected which, in turn, is influenced by other conditions such as atopy, food allergy, vaccination, and season. Clinical signs include non-inflammatory hair loss and scaling. Most dogs are young adults when first affected. There is extreme variability between breeds suggesting that this is a common end-result of potentially very different processes.
The diagnosis is confirmed with biopsies for histopathology, which should be taken from normal, mildly-affected and severely-affected skin. Carriers can sometimes be predicted by early biopsy.
The condition responds to anti-inflammatory therapies, and the best approach is frequent anti-seborrheic shampoos (including dishwashing liquid) and emollients (e.g., baby oil, propylene glycol, urea, lactic acid) and oral supplementation with high-dose marine oil. In rare cases, dogs can go into spontaneous (if only transitory) remission.
Dermatomyositis has a definite hereditary component (autosomal dominant with variable expressivity), but is also believed to be affected by infections (viral particles recovered) and an immune-mediated process. The list of breeds affected continues to grow.
Clinical signs tend to become evident by 12 weeks of age and consist of erosions and scarring on face, elbows, ears and hocks; muscle wasting is seen in some cases. Some dogs have difficulty eating, drinking and swallowing and megaesophagus may result in aspiration pneumonia. The diagnosis can be confirmed with histopathology and electromyography.
Some cases spontaneously improve so all therapies must be based on individual assessment. Vitamin E is recommended to help decrease scarring. Corticosteroids are of little benefit. Other therapies include pentoxifylline and avoiding sun exposure.
Malassezia pachydermatis, formerly Pityrosporon canis is a common saprophytic yeast found on the skin and mucous membranes of dogs. It is a common complication of atopy, pyoderma and keratinization disorders. The organism is found in the ear canals, anal sacs, vagina, perioral region, interdigital area and rectum on normal canids.
It is believed that Malassezia dermatitis is NOT a primary infection but rather an opportunistic infection. The condition is often pruritic and musty smelling with the ears, perioral area, chin, neck, feet, ventrum, thighs, and claws being preferentially affected.
The diagnosis is complicated by the fact that this yeast can be recovered from the ears of half of all normal dogs. The successful resolution of Malassezia dermatitis requires treatment of the underlying problem. Systemic and topical antifungal therapy will only "cure" the condition if the underlying disorder has been resolved.
Cyclic Flank Alopecia
The pathogenesis of cyclic flank alopecia is unknown but it bears many similarities to an endocrinopathy although no endocrine dysfunction has ever been documented. The clinical presentation is one of hair loss and hyperpigmentation of the trunk. Sometimes, there is partial regrowth and then progressive hair loss with subsequent seasons. Animals are otherwise completely healthy.
The diagnosis is still quite subjective and often based on clinical signs and breed predisposition. To date, there has been no discernible endocrine abnormality detected. Biopsies show primary and secondary follicles that are distorted and dwarfed. The best treatment is conscientious neglect. The process does not adversely affect these animals. Melatonin and etretinate are other options.
The pathogenesis of this bizarre condition is unknown but hereditary and immune-mediated processes are suspected. There is onychomadesis and onychodystrophy (onychorrhexis, onychomalacia, onycholysis) often affecting ALL claws. Pain is variable, as is incidence of lameness.
Skin scrapings and cytology are non-diagnostic but histopathologic findings in the nail bed are consistent. It is also important to screen for underlying problems such as lupus, hypothyroidism, adverse food reactions and immune deficits. Successful management requires addressing any underlying problems, but treatment with marine oils, tetracycline and niacinamide, and pentoxifylline can all be successful.
Acral Lick Dermatitis (ALD)
Acral lick dermatitis certainly is not a new disorder but treatments have changed. The exact cause is still unknown but dermatologic, behavioral and neurologic theories have been proposed. Clinically, ALD is a cutaneous reaction pattern in which dog licks at one or more limbs and cause progressive erosive-ulcerative lesions that become hyperplastic and nodular. Males are more commonly affected and most dogs are adult at onset.
The diagnosis is suggestive based on clinical presentation but it is important to screen for possible underlying problems such as dermatophytosis, musculoskeletal disorders, demodicosis, neoplasia, infection, and immune deficits. Control is achieved in about 65% of cases but that control can be accomplished with a wide variety of therapeutic modalities. Cases should first be treated empirically with bactericidal antibiotics for a prolonged period and topical antiseptics under an occlusive wrap. Topical anti-inflammatory therapies, long-term antibiotics, behavioral drugs and even electronic shock collars tend to have the best responses. An Elizabethan collar should be used when the animal is not monitored.
Superficial Necrolytic Dermatitis
Superficial necrolytic dermatitis is a metabolic dermatosis with underlying pathology such as liver disease, pancreatic cancer, diabetes mellitus etc. It is thought to involve an imbalance of amino acids, fats, and/or zinc in association with some form of liver pathology.
Clinically, there are systemic signs of disease, such as weight loss, combined with erythema, erosions, ulceration, and crusts affecting the muzzle, lips, nose, mucocutaneous junctions, feet, pressure points, ears, and perineum. It is fatal in most cases. The diagnosis can be confirmed by biopsies and ultrasound examination of the liver. Amino acid profiles, liver biopsy and glucagon levels can all be useful.
Necrolytic dermatitis is potentially fatal and most dogs die within 6 months of onset. For resolution to occur, one must address the underlying problem. Supportive care includes amino acid supplementation and specially prepared diets with supplements of zinc and relevant long-chain fatty acids.
1. Nesbitt, G; Ackerman, L: Canine & Feline Dermatology, Veterinary Learning Systems, 1998, 498pp.