Thank you for the photos. That "lump" appears to be a resolving histiocytoma - a benign growth that eventually crumbles away within 12 weeks. I can't confirm such a growth without needle aspirating it and examining the aspirate microscopically but I can say that it appears to be quite benign and of little significance. The skin on his chin and lips represents a chin pyoderma - a bacterial infection that isn't true acne but rather a traumatic furunculosis (think "boils"). Short, stiff hairs are forced backward through the hair follicle, creating a sterile foreign body reaction that may become subsequently infected. This may be induced by trauma to the chin (e.g., caused by lying on hard floors, friction from chew toys).
1) Any secondary bacterial infection should be treated with appropriate systemic antibiotics for at least 2-3 weeks. Malassezia (yeast) should be treated with fluconazole for 30 days. Antibiotics of choice are potentiated amoxicillin (Clavamox) or enrofloxacin (Baytril).
2) Hairs around lesions should be clipped, warm water compresses applied, and affected areas cleansed with human alcohol-free acne pads, or with benzoyl peroxide-, sulfur-salicylic acid-, or ethyl lactate-containing shampoo every 1-2 days until lesions resolve, then as needed for maintenance control. These shampoo can be found over the counter in pet/feed stores or at his vet’s office. Often frequent chin cleaning (every 2-3 days) is needed to prevent relapses.
3) Alternative topical products that may be effective when used every 1-3 days or on an as-needed basis include the following:
Mupirocin ointment or cream (prescription drug)
2.5% benzoyl peroxide gel (might be irritating in some cats/over the counter product)
0.01-0.025% tretinoin cream or lotion (prescription drug)
0.75% metronidazole gel (prescription drug)
Clindamycin-, erythromycin-, or tetracycline-containing topicals (prescription drugs)
The prognosis is good, but lifelong symptomatic treatment is often necessary for control. Unless secondary infection occurs - apparently it has - this is a cosmetic disease that doesn't affect his quality of life.
His pruritis (itchiness) however, may or may not indicate pyoderma on the rest of his skin. His vet will need to examine all of your dog's skin hands-on. I'm going to post my entire synopsis of the itchy dog for you so you can see what I need to consider in such a patient. Please take your time perusing it and then return to our conversation with further questions or concerns if you wish.
Pruritic (itchy) dogs are suffering from an allergic dermatitis in the great majority of cases. Allergies to flea saliva, environmental allergens (atopic dermatitis) such as pollens, molds, dust and dust mites, and foods should be considered. (Paw and extremity licking indicates both atopy and a food intolerance and so it behooves vets to distinguish one from another.) In many instances, a concomitant pyoderma (bacterial skin infection), yeast infection (Malassezia), or mange mite (Demodex or Sarcoptes) might be contributory.
Your vet can check a sample of your dog's skin surface microscopically (a “cytology”) for abnormal numbers of bacteria and yeast and skin scrapings can be taken in an attempt to find mites. Pyoderma is treated with a minimum of 3-4 weeks of an antibiotic in the cephalosporin class such as cephalexin (Keflex) plus antimicrobial shampoos containing either chlorhexidine or benzoyl peroxide and yeast is addressed with ketoconazole plus shampoos containing either ketoconazole, miconazole, or clotrimazole for at least a month.
Our dermatologists tell us to provide one of the newer prescription products available from his vet even if fleas aren’t seen. Over the counter products containing imidocloprid (Advantage, e.g.) or fipronil (Frontline, e.g.) may be ineffective because many populations of fleas have developed resistance to those chemicals. Consider products containing a different class of insecticide such as Bravecto, NexGard, Comfortis, and Vectra. New prescription products are becoming available all of the time. Dogs can be such effective groomers so as to eliminate all evidence of flea infestation. Dogs who remain primarily indoors can contract fleas because we walk them in on us and flea eggs and larva can remain viable in your home for months. As the weather warms or you turn on heaters at this time of year, egg hatches are common. If the area between the edge of your dog's rib cage and tail (the “saddle” area) is particularly excoriated, a flea saliva allergy should be the most important differential diagnosis. In severe cases, an anti-allergenic prescription glucocorticosteroidid such as prednisone will work wonders for dogs allergic to the saliva of the flea. If you have other pets they may have fleas too but may not be allergic to the flea’s saliva.
Environmental allergies (atopy) are usually initially addressed with prednisone as well. In some dogs an over the counter antihistamine such as clemastine (Tavist) at a dose of 0.025 - 0.75mg/lb twice daily or diphenhydramine (Benadryl) dosed at 1-2mg/lb twice daily (maximum dose of 50 mg at any one time) may be effective. Antihistamines, however, aren’t reliably effective. Adding fish oil to the diet at a dose of 20mg/lb daily of the EPA in the fish oil might synergize with antihistamines to provide better anti-pruritic action. The omega-3 fatty acids in fish oil are antiinflammatory but may take 8-12 weeks to kick in. The new cytokine antagonist oclacitinib (Apoquel) is likely to revolutionize how we address atopic dogs and should be discussed with his vet. Oclacitinib works as well as a steroid without a steroid's adverse effects. Please note that atopy, at least initially, should have a seasonality to it while a food intolerance should cause pruritis regardless of the season. Chronically atopic dogs may be pruritic year round.
Food intolerance/allergy is addressed with prescription hypoallergenic diets. These special foods contain just one novel (rabbit, duck, e.g.) animal protein or proteins that have been chemically altered (hydrolyzed) to the point that your dog'simmune system doesn't "see" anything to be allergic to. The over the counter hypoallergenic foods too often contain proteins not listed on the label - soy is a common one - and these proteins would confound our evaluation of the efficacy of the hypoallergenic diet. The prescription foods are available from his vet. There are many novel protein foods and a prototypical hydrolyzed protein food is Hill’s Prescription Diet z/d ultra. (I prefer the hydrolyzed protein diets because it avoids the possibility of my patient being intolerant to even a novel protein.) A positive response is usually seen within a few weeks if we’ve eliminated the offending food allergen. Food intolerance can arise at any age and even after our patient has been eating the same food for quite some time.
We need to consider seborrhea in such a patient as well. This is skin disorder of keratinization and maturation. It's a diagnosis of exclusion of the above mentioned skin disorders and can be suggested by skin biopsy.
You also have the option of having a specialist veterinary dermatologist (please see here: www.acvd.org) attend to him. You can expect some combination of skin scrapings, cytology, bacterial culture and sensitivity, fungal culture, skin biopsy, intradermal or blood allergy testing, or presumptive hypoallergenic diet trials to be performed.
Please respond with further questions or concerns if you wish.