|
Featured case study:
12-year-old neutered male
rottweiler, Tonka
by Dr. Katie Thompson
of the Veterinary Center at Fishhawk, Lithia, Florida
Detailed history
Tonka was neutered two years ago. He had
a history of immune-mediated thrombocytopenia three years ago. Six weeks prior to the emergency
presentation, Tonka presented for a routine geriatric wellness evaluation. At that time, a
complete blood count (CBC) and chemistry profile were unremarkable, with all results within
reference interval limits. A SNAP® 4Dx®
Test was negative and Tonka was current on all heartworm, flea/tick and intestinal parasite
prophylaxis as well as appropriate vaccines. Other than the presence of a large, slow-growing,
lipoma-like mass, his physical examination was also unremarkable. The owners elected surgical
removal of the lipoma (confirmed on histopathology) 10 days prior to the current emergency
presentation. Tonka’s recovery from surgery was uneventful.
Physical examination
On physical examination, Tonka was
pyrexic (T=103.9°F) and in good body condition. He was laterally recumbent and appeared moribund
with signs of shock: tachypnea, tachycardia, pale-to-white and mildly icteric mucous membranes
and weak and “thready” femoral pulses. Mild splenomegaly was present on abdominal palpation. The
surgical incision site from the lipoma removal was clean, dry and intact.
Differential diagnoses
The working clinical differential
included splenic neoplasia such as hemangiosarcoma with rupture and secondary hemorrhage,
immune-mediated hemolytic anemia (IMHA), ehrlichiosis, leptospirosis, other infectious diseases,
lead or other toxicities, trauma, drug hypersensitivity, gastrointestinal ulceration and
acute/chronic renal or hepatic failure.
Diagnostic plan
A CBC, complete chemistry profile
including electrolytes and a complete urinalysis were performed in order to assess potential
primary and secondary organ involvement. Survey radiographs were taken to investigate for
possible splenomegaly and/or abdominal hemorrhage. Pending initial findings, a saline
agglutination test and abdominocentesis were planned.
Laboratory data
Figure 1—100x oil objective field of view of the monolayer of a blood
film from a dog, Wright’s stain. Note the numerous spherocytes, the large
polychromatophil (center) and the toxic immature (band) neutrophil (lower left).
|
|
Erythron—There was a severe, minimally-to-mildly regenerative
anemia present. Elevation of MCHC (above the analyzer’s reportable range) supports the likely
presence of cell-free hemoglobin due to in vitro or in vivo hemolysis or a combination of both. A
minimal-to-mild increase in the absolute reticulocyte count was an objective indicator of bone
marrow response to a peripheral demand for erythrocytes/regeneration. Polychromasia noted on the
blood film supported the reticulocyte count reported. Other significant morphologic findings
included the presence of numerous spherocytes, marked anisocytosis and the presence of occasional
nucleated red blood cells. The presence of marked spherocytosis with no other significant
poikilocytosis strongly suggested extravascular immune-mediated hemolytic anemia; cause is not
identified. Agglutination was suggested during blood film review.
Leukon—The leukon was characterized by a moderate
leukocytosis, which was characterized by a neutrophilia, monocytosis and an insignificant
basophilia. The neutrophilia and monocytosis supported inflammation, which is commonly seen with
intravascular and extravascular hemolytic disease. Review of the blood film revealed moderately
toxic neutrophils and a mild left shift, which also support inflammation. The lack of
lymphopenia and eosinopenia made glucocorticoid influence (“stress”) unlikely, which is confusing
with this clinical presentation where “stress” was quite likely.
Thrombon—Platelet numbers are within reference interval
limits; however, the MPV (mean platelet volume) and PDW (platelet distribution width) are higher
than typically seen with dog platelets. Normally both the MPV and PDW are less than 18 fL and 18%,
respectively. The finding of larger than normal platelets on average (increased MPV) and more
variably sized platelets than normal (increased PDW) supported a bone marrow response to a
peripheral demand for platelets. Compensated peripheral destruction (possible immune-mediated
destruction) or consumption of platelets would be considered but in light of the probable IMHA,
immune destruction of platelets is most likely.
Clinical chemistry
Hepatic panel—The mild increased ALT and ALKP supported
minimal hepatocellular injury and possible cholestasis; however, changes are not severe and they
most likely represent secondary changes to the severe anemia rather than primary hepatic disease.
The minimal increased total bilirubin may represent a false-positive interference from the
hemolysis; however, both prehepatic icterus (liver conjugating capacity overwhelmed with
bilirubin from the hemolytic disease) and cholestasis must be considered also.
Urinalysis—The presence of moderate bilirubinuria in the
face of a nonconcentrated urine specific gravity supports possible minimal cholestasis.
Diagnostic summary
The marked spherocytosis with no other
significant poikilocytosis was strongly supportive of IMHA. A positive saline agglutination test
was additional support. Although no thrombocytopenia was seen, immune mediated destruction of platelets
with complete compensation was suggested due to the morphologic evidence for bone marrow response
to a peripheral demand for platelets; platelet lifespan was likely decreased.
Therapeutic plan
Initial supportive care included
intravenous fluid therapy, three blood transfusions with DEA 1.1 negative packed RBC, azathioprin
and prednisolone (slow tapering doses), famotidine, ultra-low-dose aspirin and doxycycline.
Serial laboratory data, including complete blood counts and chemistries, were included in the
monitoring plan.
Clinical case outcome
Tonka continues to do very well
several months after his diagnosis of IMHA on a low
every-other-day dose of prednisolone and
azathioprin and judicious monitoring of clinical signs and laboratory values. Serial packed cell
volume (PCV) measurements are presented in Figure 2.
Figure 2—Serial packed cell volume (PCV) measurements over the clinical
course and subsequent follow-up monitoring.
When autoagglutination is suggested on microscopic evaluation of the blood film, consider
performing a simple in-house saline agglutination test. There are multiple reported ways of
performing this assay but a simple method consists of mixing one drop EDTA anticoagulated
blood (purple-top tube) with one drop of physiologic (0.9%) saline.
The slide is then examined grossly and microscopically for signs of agglutination. Rouleaux
and nonspecific erythrocyte clumping is related to a weak electrostatic surface charge
between cells and typically disperses during the dilution process where the
three-dimensional
clumping associated with autoagglutination is related to a strong antibody cross-linking
between cells and typically remains.
In some cases where there is difficulty differentiating rouleaux from true autoagglutination,
a greater dilution with saline may be needed. The following process can be effective: Place a
drop of EDTA anticoagulated blood on a glass slide. Place a coverslip over the blood. Place
several drops of saline on the slide at the edge of the coverslip. Watch microscopically for
cell dispersion or retention of three-dimensional clumping as the saline rushes under the
coverslip and dilutes the blood to a much greater degree.
Tell us what you think of this case, or let us know if you have a case that
you would like to submit. E-mail us at
diagnosticedge@idexx.com to get the process started.
|
Create your own account on the 
This symbol indicates PDF-formatted materials. To view, you may need to 