Amyloidosis

Metabolic storage disorders usually result from the body's inability to break down some substances because of partial or complete lack of certain enzymes . The substance can build up to a toxic level, or the body is unable to produce a substance that it needs. Some metabolic disorders are caused by an increased demand for a specific element or nutrient that has become deficient under certain conditions. In hypoglycemia, the animal's metabolic reserves are unable to sustain sugar (glucose) in the blood at a level needed for normal function. The difference between production-related metabolic diseases and nutritional deficiencies is often subtle. There are a number of defective bone formation diseases of dogs and cats which result from metabolic abnormalities.

When inflammation occurs, certain chemicals are produced and released into the blood. These chemicals of inflammation are called the Acute Phase Reactant Proteins (APP). After the inflammation has gone away, the APP are broken down by the body and excreted. Dogs (or people) with amyloidosis can't break these APP down into excretable form and instead turn it into amyloid AA protein and dump it outside the cells but still within the body.

Amyloidosis is a condition that occurs when amyloid protein is deposited in various organs in the body. It is a progressive diseases that often leads to chronic kidney failure. It is mostly seen in dogs, and is rare in cats.

Some types of amyloidosis are hereditary in dogs. Others occur as a result of diseases such as heartworm infection, various cancers, or inflammatory or immune-related conditions. The inflammation in case of familial canine dermatomyositis may predispose to the development of amyloidosis. The disease can become fatal if amyloid is deposted into the tissue of critical organs, such as kidneys, liver, or heart. There are several types of amyloid, and the classification of amyloidosis is based on which amyloid protein is involved and and at least 23 types of amyloidosis have been identified in humans.

Renal Amyloidosis

Renal amyloidosis is one of the most common familial disorders in cats and dogs which include renal dysplasia, polycystic kidneys, basement membrane disorders, and tubular dysfunction (Fanconi syndrome). Dogs with renal amyloidosis usually present with clinical signs of kidney failure and include vomiting, loss of appetite, lethargy, increased thirst and urination, weight loss, and dehydration. Some dogs may have intermittent fever and joint swelling. Laboratory findings are compatible with kidney failure.

Renal Amyloidosis Is Inherited in Some Breeds

Recent studies showed that renal amyloidosis (RA) is inherited in Chinese Shar Pei dogs and that they develop RA at a younger age than other dog breeds, and that the acquisition of this trait is compatible with autosomal recessive inheritance. Familial renal amyloidosis also occurs in the Abyssinian cat. Amyloidosis has also been reported in young Siamese and Oriental Shorthaired cats. Familial renal amyloidosis in the Chinese Shar Pei dog is also called Sharpei fever or Sharpei hock syndrome as it begins with episodes of fever and swollen hocks. The fever and joint swelling are self limiting but often reoccur. Signs may develop in pups or adults.

Types of Amyloidosis

Amyloidosis can be classified as systemic or localized which is more common and can affect almost any tissue or organ in the body but is found chiefly in kidneys, liver, spleen, and adrenal gland.

There are two major forms of systemic amyloidosis. The most common form in domestic animals is reactive (secondary) amyloidosis due to chronic inflammatory diseases. In reactive amyloidosis, the deposited amyloid protein is AA type that is derived from serum (blood) amyloid A synthesized in the liver. The other form of systemic amyloidosis is light-chain (AL) amyloidosis, which is the most common type in human beings but very rare in domestic animals. One of the common underlying causes of human AL amyloidosis is multiple myeloma, which accounts for 12% to 15% of the cases.

Diagnosis of Amyloidosis

Because of its wide distribution and stealthy onset, amyloidosis is difficult to diagnose. However, your veterinarian may suspect amyloidosis if your dog has a chronic infection or inflammation and develops kidney or liver failure. Renal biopsies are needed to differentiate renal amyloidosis from immune complex-mediated glomerulonephritis (ICGN).

Treatment of Amyloidosis

There is no proven specific treatment for amyloidosis. Treatment of the underlying disease may result in regression of amyloid and associated signs. The prognosis is usually poor. Some dogs can be managed up to 1 year. Some Abyssinian cats may have no signs of the disease.

References:
REF FILE #DH-128-67