Paraneoplastic Syndrome in Dogs: Symptoms, Causes and Treatment

Paraneoplastic syndromes visible in any canine typically starts with a malignant or benign tumor.

Commonly called PNS, paraneoplastic syndromes are a group of disorders that begin from abnormal secretions of a hormone (or hormone-like product) from cancerous tumors.

The secretions impact the body's related tissues or organs and often generate an abnormal clinical response in canines dealing with cancer.

The related tissues or organs refer to those items directly related to the affected organ. Alternatively, paraneoplastic syndrome in dogs may occur due to the body's immune response to the tumor.

The response has nothing to do with the invasiveness of the primary tumor but is often the secondary response to abnormal secretions produced by the benign or malignant tumor.

The symptoms associated with this condition depend on the reaction of the organ or tissue being targeted.

Paraneoplastic Syndrome in Dogs Symptoms

As previously mentioned, the symptoms associated with this condition will significantly depend on the type of tumor within the body and the organ systems affected by the abnormal secretions from the tumors.

This disorder is most frequently connected with a malignant tumor, although it occasionally results from a benign tumor that secretes hormones. Remember, a benign tumor is far rarer than a malignant type.

Physical symptoms of paraneoplastic syndrome in dogs include the following:

• Hair loss or alopecia
• Anemia
• Loss of weight and physical wasting
• Intestine or stomach ulcers
• Low blood sugar levels (hypoglycemia)

Causes of Paraneoplastic Syndrome in Dogs

PNS results in chemical changes within the bodily structure or function that don't directly relate to the primary tumor or metastasis.

This condition primarily stems from tumor production of small molecules (for example, cytokines or hormones). Sometimes, a patient's first indication of cancer is the presenting PNS, making it essential to recognize.

Knowing what cancers hold a differential list can also help. Should the tumor be treated successfully, the PNS should resolve.

Understanding Paraneoplastic Syndromes (PNS)

Paraneoplastic syndromes (PNS) are systemic disorders resulting from cancer but aren't related to the tumor's location, size, or metastasis.

It's also not associated with the physiological activities of the normal, mature tissue of origin.

Treatment options for PNS relate to the underlying neoplasia, with all recurrence of PNS signaling tumor recurrence.

These conditions start from the production and release of substances (hormones, peptides, growth factors, and cytokines) that are typically not produced by the originating cell of the tumor.

Alternatively, these substances are being made in extreme amounts.

PNS can occur distant from cancer or may result from proteins produced by normal cells. The stimulation of immune response leading to autoimmunity may occur.

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Issues of Paraneoplastic Syndrome

Hypercalcemia of Malignancy

The most probable cause of hypercalcemia in dogs is hypercalcemia of malignancy (HM). A cancer work-up should be done for any animal presenting these symptoms unless an apparent non-neoplastic reason is identified.

The most common tumors associated with HM are lymphoma, anal sac apocrine gland adenocarcinoma (AGASACA), thymomas, and multiple myeloma.

In T-cell lymphoma, approximately half of dogs are diagnosed with HM. Additionally, close to 25% of dogs with AGASACA have HM too.

Currently, the most common cause of hypercalcemia of malignancy (HM) is the tumor's production of parathyroid hormone-related peptide (PTHrP), although several other cytokines can cause this.

The most common symptom with canines struggling with hypercalcemia is polyuria/polydipsia (PU/PD). Should a dog present with hypercalcemia, a veterinarian should perform a cancer screen.

A thorough exam is standard, with particular attention to the peripheral lymph nodes, rectal exam, and emptying of anal sacs.

Steroids should never be used for calciuresis until leukemia and lymphoma are ruled out. Ideally, removal of the underlying cause (through chemotherapy or surgery) is the most effective way to treat HM, with close monitoring of calcium afterward.

Hypoglycemia

The overproduction of insulin from insulinoma is the most common cause of paraneoplastic hypoglycemia.

Diagnosis of insulinoma involves documenting normal or elevated levels of insulin.

Other types of tumors and leiomyomas and leiomyosarcomas have been associated with hypoglycemia.

Patients with a large tumor in lymphoblastic leukemia could be hypoglycemic due to excessive glucose consumption.

Hypertrophic Osteopathy

Hypertrophic osteopathy (HO) is another disorder that causes periosteal proliferation of the long bones. Most commonly, it is usually bilateral and will typically start on the digits and move proximally.

This condition is generally seen in canines with primary lung tumors or pulmonary metastasis (particularly metastatic osteosarcoma).

Patients with swollen, painful limbs and difficulty ambulating commonly face HO. The pathogenesis isn't well understood.

For dogs with primary lung tumors, surgery can typically resolve HO. Unfortunately, a metastasectomy isn't recommended when a dog presents with pulmonary metastasis.

Hyperglobulinemia or Hyperviscosity

Hyperglobulinemia occurs when a tumor cell overproduces immunoglobin. This is most commonly seen in dogs with multiple myeloma.

Patients presenting with elevated globulins on bloodwork may warrant additional work-up.

A thoracic radiograph should be performed to identify a monoclonal gammopathy. The overproduction of immunoglobulins can lead to hyperviscosity syndrome.

This syndrome will cause sludging of the blood in small vessels, bleeding diatheses, and inability to deliver oxygen.

How to Diagnose Paraneoplastic Syndrome in Dogs

You'll need to give a thorough and comprehensive history of your pet's health, including the onset of symptoms.

This information could help your veterinarian determine which organs are causing secondary symptoms.

Once the vet finishes with the physical examination, they will perform a complete blood count and urinalysis.

This testing will return evidence of an immune system response to cancer and may also measure the impact the tumor secretions have on various tissues and organs.

Imaging studies like radiographs of the thoracic cavity can rule out cancer of the lungs and abdomen, along with any organs situated within the imaging.

An ultrasound image is also used to examine the structure of the internal organs and adrenal glands. Various biopsies of impacted organs may be taken to aid further diagnosis, especially if skin disorders are present.

Differential Diagnosis

Alternative diagnoses may exist, depending on the condition. Pregnancy, heartworms, cardiac disease, granuloma, pneumonia, abscess, and foreign bodies are all alternative considerations.

HO may be the first indicator of neoplastic disease. Treatment with anti-inflammatory doses of prednisone may ease swelling and pain. Bisphosphonates may also be beneficial.

In animals with no signs of alternative infection, fever may lead to a PNS diagnosis. Tumor cells occasionally release pyrogens, but diagnosis by exclusion of other causes of fever is preferred.

Treatment of Paraneoplastic Syndrome

Additional nutritional support is required if your dog is suffering from wasting or anorexia.

The treatment of these conditions will be highly individual, depending on the tumor's location, type, and stage.

A dog must be stable to continue with invasive treatments. Most of the time, invasive treatments are necessary.

This treatment is often because the tumor is often highly malignant. The veterinarian will remove the tumor whenever possible.

Chemotherapy may also be a treatment option. However, it is only reserved for tumors that will likely respond to chemical therapy.

The veterinarian will probably discuss these options with you during treatment. Occasionally, for some patients that cannot treat the underlying tumor, management of the clinical signs and treatments to improve life quality is often planned.

Living and Management of a Dog with PNS

The overall prognosis depends significantly on the location of the underlying tumor and the treatment.

Unfortunately, the malignant nature of tumors and a diagnosis of paraneoplastic syndrome will often lead to a fatal outcome.

Paraneoplastic Syndrome in Dogs: Conclusion

All paraneoplastic syndromes are defined as any systemic disorders resulting in the presence of cancer. These conditions aren't related to the tumor's size, metastasis, or location.

These disorders aren't associated with the physiological activities of the standard and mature tissues of origin.

Most of these conditions result from the production and release of various substances (cytokines, hormones, peptides, and growth factors) that aren't typically produced by the cell of origin.

Unfortunately, treatment of PNS will directly relate to the underlying tumor.

Due to its malignant nature, a diagnosis of the paraneoplastic syndrome will often lead to a fatal outcome.

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