Calcinosis cutis in dogs is a deposit of insoluble mineral salts in different layers of the skin. These mineral deposits will cause dystrophic or metastatic calcification, the most commonly affected areas can be the back, underarms and groin.
Calcinosis cutis lesions commonly appear on the skin as bumps or flat raised areas (papules or plaques) with gritty yellow, white, or grey granules. The lesions are commonly surrounded by reddened skin, because calcinosis cutis often causes inflammation.
The most probable immediate cause is an increase in the blood enzyme lipase, which leads to degeneration of the subcutaneous adipose tissue (fat), followed by calcification of the degenerated tissue. 
The most common cause of metastatic calcinosis cutis in dogs is overproduction of adrenal hormones (corticosteroids or "steroids").
This may be due to overgrowth or cancer of the adrenal glands or of the pituitary, the gland that controls the adrenals.
In these cases, we may find ourselves in the presence of another pathology or contributing cause, Cushing's syndrome.
Other, rare causes of metastatic calcification can be kidney disease (common cause in cats), malignant tumors producing abnormal hormones that increase blood calcium concentrations (e.g. tumors of the lymphoid system and glands of the anal sac), diabetes mellitus and lung disease..
The most common symptom is hard lumps that form under the skin, in the mouth or on the footpads, we can observe too:
Clinically, the appearance of the skin lesions may lead to suspect calcium deposits as the problem, particularly when the age, breed and clinical history are considered.
Blood tests can help indicate some underlying primary conditions, but for confirmation, it may be necessary a biopsy, when Cushing’s disease is suspected, there are confirmatory tests to diagnose this disease such as an ACTH stimulation test or Low Dose Dexamethasone Suppression Test and an abdominal ultrasound.
The usual treatment for calcinosis circumscripta and single areas of calcinosis cutis is surgical removal. Additional treatment for calcinosis cutis will depend on the underlying cause.
In fact the lesion tends to resolve spontaneously once the underlying cause is identified and treated in a time frame of 3 to 12 months.
Additional treatments can include non-steroidal medications to reduce itching, antimicrobial shampoos to decrease the risk of future infection, and/or oral minocycline and aluminum-based antacids to help bind calcium.
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