Image Quiz: What is causing these skin lesions?

A 2-year-old, female, spayed, French bulldog has no previous history of skin disease but has developed these skin lesions over the past one to two months. The only current medication is 0.5 mg/kg/day of prednisone prescribed by a neurologist for the last six months due to disc disease. The lesions are non-pruritic and firm on palpation.

What is your most likely diagnosis based on these images?

• A. Deep pyoderma
• B. Calcinosis cutis
• C. Dermatophytosis (ringworm)
• D. Demodicosis

The answer is B (calcinosis cutis). All of the answers should be on your differential diagnosis list, but the most probable cause of the lesions is calcinosis cutis. Calcinosis cutis is a depositional skin disease in which calcium salts are deposited in dermal tissues. This is because of altered calcium metabolism and inappropriate deposition of inorganic calcium and phosphate ions in the skin and subcutis. Basic diagnostic tests such as cytology, skin scrape, and fungal dermatophyte test medium/culture should be performed to rule out other possibilities. A skin biopsy will confirm the diagnosis.

What disease is the most common underlying cause of calcinosis cutis?

• A. Hypothyroidism
• B. Pemphigus foliaceous
• C. Cushing’s Disease
• D. Cutaneous lymphoma

The answer is C (Cushing disease). The most common underlying cause is hyperglucocorticoidism, or elevated levels of steroids in the body. This is often the result of a metabolic disease or imbalance such as Cushing disease, which causes the body to produce too much internal cortisol—or long-term therapy with corticosteroids. In this case, the steroids were used for back pain, but we will often see calcinosis cutis develop in dogs on steroids for allergies, chronic skin conditions, autoimmune/immune-mediated diseases, irritable bowel disease, and neoplastic diseases.

The best treatment is to remove the underlying cause. In this case, we would need to taper and eventually stop the oral steroids. With the help of this patient’s neurologist, we are tapering the steroids and starting alternative medications for the back pain. In the case of Cushing disease, the disease needs to be treated with trilostane or mitotane. Addressing the secondary bacterial infections is very important because the skin often ulcerates during resolution of the condition. A skin culture is recommended to determine the best antibiotic to treat the secondary deep pyoderma. DMSO (dimethyl sulfoxide; 90% gel) can be used topically, because this may increase calcium mobilization to the skin surface and/or systemic absorption.

Overall, the prognosis depends on the underlying cause and how advanced the skin condition has become. The skin can return to normal in some cases, but if dermal ossification (essentially the skin becoming bone) has occurred, it will be difficult to reverse the skin changes.

Judy Seltzer, BVetMed, MRCVS, DACVD, graduated from the Royal Veterinary College in London, England, and completed her residency in dermatology at the University of Florida in Gainesville. She has been working in her home state of New York since 2009, currently at BluePearl Veterinary Partners in New York City. She and her husband have a baby girl and 4 cats and enjoy traveling, fall festivals, winter activities, and dining out.