A few weeks ago I released the first of this two-part series on paraneoplastic syndromes. If you haven't read it yet, you can check it out here. Just to refresh, a paraneoplastic syndrome is a cancer-associated change that can occur in a patient distant to the actual tumor.
In many cases, the paraneoplastic syndrome (PNS) is the first sign of cancer, so being able to recognize it can lead to an early diagnosis (and potentially a better outcome).
As mentioned in Part 1, the PNS will often parallel the underlying cancer. So if the underlying cancer is in remission or removed, the PNS will resolve. If we later see return of the PNS, we will likely find return of the cancer on further investigation as well. PNS can be very helpful in monitoring the remission status of a patient.
In Part 1 we discussed cancer cachexia, gastroduodenal ulceration, hypercalcemia, hypoglycemia, and fever. All of these paraneoplastic syndromes were explained and discussed in detail.
In this article, we'll discuss anemia, hypertrophic osteopathy, and myasthenia gravis.
Anemia (reduced red blood cell count) is common in veterinary cancer patients. It is most commonly due to something called anemia of chronic disease (ACD), but can also be caused by immune-mediated hemolytic anemia (IMHA) and other conditions that I won't describe here.
Anemia of chronic disease is not life threatening. We typically recommend treating the underlying cancer. IMHA on the other hand, can be life threatening and involves the patient's immune system destroying red blood cells. Treatment involves removing the underlying tumor/treating the underlying cancer, but often also involves hospitalization and treatment with blood transfusions, steroids and immunosuppressants.
Hypertrophic osteopathy (HO) involves the development of new bone (periosteal proliferation) and typically starts in the digits and progresses to long bones (although other bones may be affected).
This can occur with either benign of malignant tumors but is most commonly noted with primary lung tumors (cancer starting in the lung) and pulmonary metastasis (cancer spreading to the lung from another organ).
Dogs with HO are usually reluctant to move, may have a shifting leg lameness, the affected areas are warm to the touch and may be swollen. These dogs are exceedingly painful and may also have a fever (due to pain).
The diagnosis is easy - there are classic changes on radiographs (see below).
When possible, the primary tumor should be removed. There have been reports of HO resolving if the primary tumor is successfully treated. When this isn't possible, palliating the signs involves treating pain with medication such as NSAIDs, gabapentin, etc. I've also had success in providing comfort by adding acupuncture to the analgesic regimen. It's now also common to treat with zoledronate (monthly injectable bisphosphonate).
Myasthenia gravis (MG) is a disorder involving the failure of signals to transmit appropriately from nerves to muscles. This occurs because specific antibodies are produced to receptors at the neuromuscular junction. Diagnosing this disease involves finding evidence of antibodies to these receptors using a blood test.
The most common tumor associated with myasthenia gravis is thymoma (a large tumor that forms in the chest, in front of the heart), but it has also been reported to occur with lymphoma, osteosarcoma and other cancers in dogs.
Myasthenia gravis is not always a paraneoplastic syndrome; there are other causes, for example, some dogs are even born with this condition.
What do dogs with myasthenia gravis look like? Signs include weakness (mild to severe), exercise intolerance, and difficulty swallowing. Many dogs with myesthenia gravis will also have megaesophagus.
Megaesophagus is diagnosed with radiographs; the esophagus appears much wider than normal. The clinical consequence of megaesophagus is that the esophagus doesn't function appropriately to help guide food from the mouth to the stomach. Food will often just sit in the esophagus and the patient will frequently regurgitate.
These patients often develop aspiration pneumonia because food particles are inhaled instead of swallowed during regurgitation, which is can be fatal.
To decrease the risk of megaesophagus it is recommended that patients are fed small "meatballs" of canned food upright in a Bailey Chair. Families are then instructed to have their dog sit in the chair for about 30 minutes after each feeding to increase the chance of the food actually reaching the stomach.
The image below is an example of a Bailey Chair (from vcahospitals.com) allowing for upright feeding.
Megaesophagus can resolve if the primary tumor is removed or successfully treated, but doesn't always (unfortunately!).
There are MANY other paraneoplastic syndromes that help vets and oncologists diagnose cancer - too many to cover in these articles. I hope you found learning about a few of these conditions helpful.
Dr. Lori Cesario
Board Certified Veterinary Oncologist
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