31 Oct 2016
Fiona Adam and Paula Valiente investigate the possible causes and methods of treatment for collapse episodes in a senior dog.
Figure 3. The patient has suffered no further collapse episodes (three months post-presentation) and is back to full health.
A nine-year-old male neutered cocker spaniel from south-east England is presented for further investigations after three collapse episodes over a two-week period. The dog has been in the owners’ possession from nine weeks of age. Its diet consists of a commercial adult dog kibble, it has no travel history outside the UK and is vaccinated, with occasional parasiticide treatment (none within the past three months).
During these episodes, the dog was reported to become “glazed”, then move to a recumbent position and become unresponsive, with involuntary eye movements. The owners reported spontaneous recovery from episodes within three to five minutes, after which the dog would return to its previous activities. The episodes had no apparent relationship to feeding, exercise or excitement, and no neurological abnormalities were reported between episodes.
Accurate distinction of seizure activity from syncope, weakness or other collapse causes can be challenging; however, seizure activity was considered more probable from the owners’ description.
The last collapse episode occurred one week prior to presentation. Physical examination was unremarkable, as was neurological examination.
Syncope, seizures and episodic weakness can be caused by systemic disease, such as metabolic, haematological and endocrine abnormalities, and, therefore, in the absence of examination findings to support neurological or cardiovascular cases, haematology and biochemistry were performed to further investigate (Table 1). Abnormalities identified included thrombocytopenia, which was confirmed on smear examination, and a marked hyperglobulinaemia with mild hypoalbuminaemia (Table 2).
A full history also suggested the dog was lethargic, possibly for several months. A cough (suspected to be non-productive) had also been noted. The dog was less enthusiastic about exercise, but exercise tolerance was unchanged. No change in weight or gastrointestinal signs were described and haemorrhage had not been noted from any site.
The marked hyperglobulinaemia was deemed to be the most important finding and further understanding of its cause would help to determine the cause of the patient’s lethargy, cough and collapse episodes.
Globulins in the blood include acute phase proteins, immunoglobulins and complement. Acute phase proteins are those whose concentrations change during the inflammatory response. Positive acute phase proteins are produced in increased quantities by the liver following stimulation by proinflammatory cytokines; examples include C reactive protein, serum amyloid A, haptoglobin and α1 acid glycoprotein. Negative acute phase proteins are found in lower concentrations in inflammation; examples include albumin and transferrin.
Hyperglobulinaemia can occur for several reasons. An important point to discern is whether the globulins alone are elevated, or if albumin is also elevated. Dehydration will cause non-selective elevation of all protein levels, as the fluid content of plasma will be decreased, concentrating the proteins further. Dehydration would be expected to increase both albumin and globulin concentrations, and the magnitude of the increases should be relatively small.
Accompanying erythrocytosis, pre-renal azotaemia and highly concentrated urine may also be seen alongside protein concentration elevations in dehydration to offer further clues.
In this case, hyperglobulinaemia without concurrent hyperalbuminaemia was present, meaning increased protein synthesis is present rather than dehydration.
The two main explanations for increased globulin production are a response to inflammation, or lymphoproliferative disease. Hyperproteinaemia secondary to inflammation can occur in infection (bacterial, viral, fungal, protozoal), immune-mediated disease, neoplasia or necrosis. Acute phase proteins and/or delayed-response proteins (complement and immunoglobulins) can be increased. Hyperglobulinaemia in lymphoproliferative disease occurs due to clonal populations of neoplastic plasma cells (multiple myeloma) or B cell lymphocytes (lymphoma and leukaemia) producing structurally identical globulins.
Further analysis of this dog’s serum would allow determination of the types of protein contributing to the hyperglobulinaemia and whether an inflammatory response or lymphoproliferative disease was responsible. The test that will allow this distinction is serum protein electrophoresis.
Electrophoresis separates the proteins in blood (or other body fluids) on the basis of size and electrical charge. The sample fluid is applied to a gel base, which contains an alkaline buffer. In this alkaline environment, all proteins have a negative electrical charge. An electrical current is then passed across the gel medium for a set time period. The proteins in the sample fluid migrate from the application point towards the positively charged anode. The distance a protein travels is determined by its electrical charge, size and shape. The gel is then stained to reveal a series of bands across the gel. A densitometer quantifies the amount of protein in each band by determining its absorbance of light. This information is translated into a series of peaks called an electrophoretogram.
Albumin has a strong negative charge and is one of the smallest proteins in serum, so it migrates furthest in the gel. The remaining proteins are grouped into broad categories/fractions (α1, α2, β1, β2, ϒ) using the peaks on the electrophoretogram. The area under the curve in each fraction can then be calculated as a percentage of the total and the absolute quantity of each protein fraction can be calculated using the percentages and the total protein concentration. These absolute values can be compared to reference values for each species. Protein electrophoresis results are, therefore, both qualitative and quantitative:
Acute-phase response, an immune response to inflammation, characterised by an increase in α globulins, and often a mild reduction in albumin (negative acute phase protein).
Serum protein electrophoresis was performed in this case, and showed marginally reduced albumin, mild increases in the α1 and α2 fractions (consistent with acute-phase response) and a marked polyclonal increase in the β fraction (Table 3; Figure 1). This would support an inflammatory focus as the cause of the hyperglobulinaemia, rather than a lymphoproliferative disease. Potential causes include infections, immune-mediated disease, neoplasia (non-globulin producing) or necrotic tissue.
Clinical signs reported in addition to the suspected collapse episodes were lethargy and cough. Lethargy is a non-specific finding, potentially secondary to many problems. A cough, however, would support either a cardiac or respiratory disease. No murmur or arrhythmia was present on thoracic auscultation, making congestive heart failure unlikely.
Thoracic radiographs were performed under sedation to allow further investigation (Figure 2) and showed a severe diffuse interstitial lung pattern, with a lesser bronchial component. The cardiac silhouette and lobar vessels were unremarkable. Differentials for these radiographic findings would include infection (bacterial, viral, parasitic), immune-mediated (eosinophilic bronchopneumonopathy among others) or, less likely, a diffuse neoplastic process.
In light of the abnormal thoracic radiographs, thrombocytopenia and hyperglobulinaemia, an antigen blood test was performed to investigate the possibility of angiostrongylosis; the result was positive. The test has excellent specificity; therefore, a false positive was considered unlikely.
The incidence of angiostrongylosis among vet-visiting dogs in south England, in a large epidemiological study (Schynder et al, 2013), was reported to be 1.9% to 3.2%. Hyperglobulinaemia is reported to be present in 42% to 70% of angiostrongylosis cases (Chapman et al, 2004; Gallagher et al, 2012).
Typically, the magnitude of the hyperglobulinaemia is less dramatic than present here, but marked hyperglobulinaemia secondary to angiostrongylosis has been reported (Glaus et al, 2010). Hypoalbuminaemia and thrombocytopenia, as seen in this case, are also frequently reported in angiostrongylosis.
Around a quarter of dogs with clinical signs of angiostrongylosis present with a history of collapse episodes (Chapman et al, 2004). Collapse causes can include syncope due to pulmonary hypertension, intracranial haemorrhage, or less likely, aberrant larval migration into the CNS or myocardium.
Pulmonary hypertension occurs in around 15% of dogs with angiostrongylosis (Borgeat et al, 2015) and can cause syncope. Radiographic signs of pulmonary hypertension can include right-sided cardiomegaly and distension of pulmonary and lobar arteries – none of which were present in this case. Radiography is, however, recognised as an insensitive tool for the detection of pulmonary hypertension and, therefore, cannot be excluded without further investigations, such as echocardiography.
Angiostrongylosis is regularly associated with a coagulopathy, suspected to be due to disseminated intravascular coagulation. Thromboelastography is the best method of identifying this hypocoagulation and neither platelet count nor standard coagulation times correlate well with the risk of haemorrhage in these patients (Adamantos et al, 2015; Gallagher et al, 2012).
Intracranial haemorrhage cannot be excluded in this patient as a cause of seizures, although neurological abnormalities were not present on examination. Brain MRI would allow further investigation of the possibility of intracranial haemorrhage, but was not performed in this case, given the lack of impact this would have on case management.
A third consideration for the mechanism of this dog’s collapse episodes is hyperviscosity syndrome (HVS). HVS is the constellation of clinical abnormalities that develop when blood becomes viscous/resistant to flow. Clinical manifestations are a result of decreased blood flow to tissues and sludging of blood in vascular beds and signs include seizures, retinal detachment, haemorrhage (epistaxis, spontaneous gingival haemorrhage due to a reduction in platelet function), development of renal disease or, rarely, congestive heart failure.
HVS can occur in hyperglobulinaemia, elevated cell counts (erthrocytosis or leukaemia), or where cells present have reduced deformability, such as sickle cell disease in humans. In veterinary medicine, HVS is most commonly seen with hyperglobulinaemia and erythrocytosis. Plasma/serum viscosity can be specifically measured using viscometers, but this is
rarely performed in veterinary medicine. The impact on the plasma/serum viscosity in hyperglobulinaemia is, in part, determined by the type of globulin involved, as they have different molecular weights and structure; therefore, the precise globulin concentration at which HVS develops is case dependent. Individual patients tend to have quite consistent “symptomatic thresholds”, where globulin concentrations beyond a certain point will reliably be associated with HVS.
HVS in dogs is most commonly associated with multiple myeloma, but has been rarely reported secondary to both Ehrlichia (Hoskins et al, 1983) and leishmaniasis (Proverbio et al, 2016).
Although hyperglobulinaemia is common in Angiostrongylus vasorum infection, hyperglobulinaemia as marked, as was seen in this case, is rarely reported, and HVS is a potential aetiology of this dog’s collapse episodes.
The ideal therapy for emergency treatment of HVS due to hyperglobulinaemia is plasmapheresis. This reduces plasma viscosity promptly, preventing further damage to the retinas and brain, while therapy is instituted to address the underlying cause of the hyperglobulinaemia. Unfortunately, plasmapheresis has very limited availability for use in dogs in the UK at this time.
Further investigations showed no evidence of concurrent infections, or other explanations for this dog’s clinical presentation. Treatment with topical imidacloprid/moxidectin led to resolution of clinical signs and clinicopathological abnormalities. The dog remains on long-term Angiostrongylus prophylaxis and has had no further collapse episodes (Table 4; Figure 3).
