Monday, December 5, 2011

When Repeating Diagnostics Makes Sense

By Beth Davidow, DVM DACVECC 

Many times clients will ask why we are repeating a test.  It does seem that if you have just had blood work done recently, things shouldn’t be that different.  However, when an animal is sick, things can change dramatically over a period of hours.  The following case is a good example.

A seven and a half-year-old pointer was referred to our ICU for care of a suspected reaction to a chemotherapy drug.  A review of his case showed that the dog had a skin lump that turned out to be an atypical form of a cancer called lymphoma.  (Lymphoma is a cancer of lymph nodes and lymphatics and doesn’t usually show up as a skin nodule.)  Initial screening showed no evidence of the cancer anywhere else.  The dog had been given a chemotherapy drug three weeks prior to presentation.  The tumor shrank dramatically in size and he seemed to feel well.  Many chemotherapy drugs can suppress the body’s infection fighting cells, the white blood cells, and this did happen seven days after the drug was given.  The dog was put on antibiotics and seemed to be fine.  However, three weeks after the drug was given, the dog acutely started having vomiting, diarrhea and was severely weak.  He had a fever and a borderline low white blood cell count.  Bloodwork, radiographs and ultrasound were done and no evidence was seen of any new cancer.  It was assumed that he had an infection secondary to having the low white blood cell count.

When the dog arrived at ACCES, he was dehydrated, weak and had a fever.  He had been started on IV fluids, antibiotics and anti-nausea medications at the regular veterinarian and those treatments were continued.  However, at 10:00 pm he was still febrile and now couldn’t stand up.  A blood glucose (blood sugar) was rechecked and had fallen to a dangerously low level. He was given IV glucose and was much brighter.

Why did the blood glucose fall in only 12 hours?  Normally dogs can maintain their blood sugar in a normal range even if they aren’t eating.  In the face of overwhelming infection, sometimes the bacteria are “stealing” the glucose and blood values will fall quickly.  Sometimes, if the body’s normal stress mechanisms aren’t working, it can also fall.  Sometimes, tumors can also “steal’ glucose but we hadn’t found any new cancer.  Our working hypothesis was that we still weren’t on top of the infection.  We started an additional antibiotic.

Over the next 24 hours, the glucose stayed normal and the fever resolved but the dog was still very depressed and wouldn’t eat.  The next morning, 48 hours after the initial illness started, small pinpoint bruises were noted on the skin.  This can be a sign that the clotting system isn’t working.  We checked the clotting blood values and found that the platelets, small particles in the blood that make the initial clot, were now very low, even though they had been OK the day before.  A full complete blood count was sent to the lab.  A falling platelet count can also be a sign of infection or emerging cancer but the fever was under control.  What was happening?

In the afternoon, we had our answer.  The complete blood count, which had only normal blood cells 48 hours before, now showed cancer cells in the blood.  The cancer, despite being gone from the skin, had lodged in the bone marrow and in a 48 hour period and multiplied fast enough to be found in the blood stream.  The dropping glucose and platelets were not from a chemotherapy reaction or from infection but from the emerging cancer we couldn’t yet see.

Thus, repeating the same tests several times allowed us to diagnose the reemerging cancer quickly.  It was a lesson of how rapidly things can change in the body. 

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