Anemia Due To Bone Marrow Failure (Or Toxicity) in Dogs

Anemia is defined as a reduction in the normal number of red blood cells. All types of blood cells originate in the bone marrow, so healthy bone marrow will respond to a low blood cell count by producing more. If the body is unable to adequately generate replacement blood cells, this is called non-regenerative anemia. Dysfunctional bone marrow is one of the most common causes. When bone marrow is unable to adequately produce all types of blood cells, including precursors to white and red blood cells as well as platelets, anaplastic anemia results. In dogs, this can happen due to an underlying bone marrow disease, as well as toxic ingestion, long term use of certain drugs, and some infections. Treatment will need to focus on rectifying the disease or condition which caused the imbalance, and recovery will depend on the type and severity of the problem.

Bone marrow that is not working properly is unable to adequately regenerate blood cells. This leads to a condition defined as anaplastic anemia. In dogs, anaplastic anemia develops secondary to a number of diseases and underlying conditions. Treatment and recovery will depend on the cause.

Symptoms of anemia due to bone marrow failure, typically develop slowly. The body will adjust to the low blood cell count and continue to function normally as long as possible. As the condition progresses, symptoms will become more pronounced, especially if the problem is due to a cancerous condition like leukemia. Take your dog to see a veterinarian if you notice any of the following signs:

• Poor Appetite
• Weight loss
• Lethargy
• Lack of stamina
• Weakness
• Rapid heart rate (tachycardia)
• Rapid breathing (tachypnea)
• Paleness of the mucus membranes, especially notable around the gums
• Blood in the stool
• Petechiation (a purplish spot on the surface of the skin)
• Fever
• Vomiting
• Diarrhea
• Disorientation
• Lack of coordination
• Seizures

Types

Several different types of bone marrow conditions lead to non-regenerative anemia:

• Aplastic anemia – the most general term for anemia due to bone marrow failure or toxicity characterized by lack of production of all types of blood cells.
• Pure red cell aplasia (PRCA) – only the erythroid line, the tissue that leads to the production of red blood cells, is affected. Hormone replacement drugs (recombinant human erythropoietin) as well as autoimmune responses are often the source.
• Leukemia – several different types of leukemia (sometimes called myeloproliferative diseases) cause the production of cancerous white blood cells. These are relatively rare in dogs. In acute forms, abnormal cells called blasts infiltrate the bone marrow and halt the production of normal blood cells.
• Myelodysplasia – a pre-leukemia condition in which blood stem cells produced in the bone marrow are unable to properly develop. It often develops into leukemia.
• Myelofibrosis – in this condition the bone marrow is replaced with fibrous tissue. It can occur secondary to leukemia, as well as parasite infections and some types of drug therapy.

Sometimes there isn’t an obvious cause for bone marrow failure, especially if it is due to a cancerous condition. Other times the condition can be traced to a treatable cause. These are some of the most common sources:

Infection

• canine parvovirus
• ehrlichiosis

Medical treatments

• chemotherapy drugs
• some antibiotics
• estrogen replacement
• methimazole (hyperthyroid drug)
• fenbendazole (roundworm treatment)
• phenylbutazone (pain medication)

Other factors

• Toxin ingestion
• Cancerous tumor in another part of the body
• Radiation therapy
• Autoimmune response
• Hereditary 
• Idiopathic (unknown)

A complete blood cell count (CBC) will evaluate the severity of the anemia and sometimes blood tests can indicate the source of the problem as well. Urine samples can suggest dysfunction in various body systems and the veterinarian may also ask for a feces sample. A bone marrow biopsy or aspiration will be required to evaluate the condition of the bone marrow. These procedures involve inserting a hollow needle into the bone marrow in order to obtain a sample that can be analyzed microscopically. Sedation or general anesthetic will be necessary for either of these tests.

The veterinarian will need to know your dog’s complete medical history and any drugs he is taking or has taken in the past. A detailed description of the symptoms, including the time of onset and severity, is very important. X-rays or other tests could be required depending on the suspected cause.

Treatments can vary widely depending on the cause. Antibiotics will be given to treat infection, while prednisone or a similar immune-suppressant may be prescribed if the problem is believed to be immune mediated. Medication will be given to stimulate the production of white blood cells until the bone marrow has fully recovered and blood transfusions may be necessary to help the body bounce back.

Symptoms of leukemia will also be managed with antibiotics to counter the depleted immune system and blood transfusion. Chemotherapy may be ordered to try to kill the abnormal cells. The response rate for severe forms of leukemia is only around 30% and most dogs that did respond were only in remission for about 4 months. This type of treatment can reduce symptoms and help your dog survive a bit longer.

If another medication is responsible for the problem, the veterinarian will try to reduce the dose or find another drug with does not lead to toxicity. Effectiveness will depend on the medication and the severity of the condition.

Your dog may make a full recovery from some mild infections or treatable autoimmune responses. If cancer is the root of the problem, treatment will probably involve managing the symptoms as long as possible and eventual euthanasia. Some toxicity cases are reversible once the problematic drug is discontinued. Discuss the side effects of any long-term medication your dog is taking, and evaluate positive and negative effects to determine if it is worth the risk. Frequent blood tests can help your veterinarian monitor the problem before symptoms become severe or irreversible. Regular check-ups and testing is the best way of diagnosing anemia before symptoms become apparent.