Vacuolar hepatopathy is a common hepatic disorder in dogs that typically is associated with glucocorticoid excess. In an unpublished review of 500 hepatic biopsy specimens obtained from client-owned dogs examined during the past 7 years at the Cornell University Hospital for Animals, for instance, we found that 95 (19%) had VH.
Vacuolar hepatopathy was first linked with glucocorticoid use in 1975,1 and since that time, clinicopathologic and morphologic abnormalities in dogs with naturally occurring and experimentally induced VH have been well characterized.1–12 Dogs with VH secondary to exogenous glucocorticoid administration or high endogenous glucocorticoid concentrations typically have hepatomegaly and other clinical signs of glucocorticoid excess (eg, polyphagia, polyuria, polydipsia, cutaneous changes, and a propensity for infection). In addition, affected dogs usually have high serum ALP and GGT activities and high serum concentrations of haptoglobin and cholesterol.1–12 However, although induction of the glucocorticoid-ALP isoenzyme as a result of glucocorticoid excess has been well characterized, this isoenzyme can also be induced by physiologic stress (eg, stress associated with acute or chronic illness). Thus, measurement of glucocorticoidALP isoenzyme activity has limited utility in the diagnosis of glucocorticoid-related illnesses.13–22
It has become routine to implicate glucocorticoid treatment or HAC as the underlying cause in dogs with histologically confirmed VH. We hypothesize, however, that VH is similar to glucocorticoid-ALP isoenzyme activity, in that it may be induced by phenomena unrelated to excess glucorticoids.23,24 Thus, we propose that a histologic finding of VH is, itself, insufficient to incriminate exogenous glucocorticoid administration or HAC as the underlying cause. To that end, we wanted to identify etiopathologic abnormalities in dogs with histologically confirmed VH. Specifically, the purposes of the study reported here were to determine underlying disorders in dogs with VH, to determine whether dogs with VH routinely had evidence of endogenous or exogenous glucocorticoid exposure, and to determine whether histologic distribution and severity of VH lesions could be used to predict steroidogenic hormone exposure.
Criteria for Selection of Cases
Medical records of the Cornell University Hospital for Animals were electronically searched to identify all dogs examined between 1993 and 2005 in which a histologic diagnosis of VH, steroid hepatopathy, glucocorticoid hepatopathy, hepatocellular degeneration, hepatocellular steatosis, or hepatocellular lipidosis had been made. Tissue sections for each case identified through this search (n = 610) were reviewed by one of the authors (SAC), and cases were included in the study if hepatocellular features characteristic of VH were verified.9 In addition, H&E-stained sections of hepatic specimens were examined at 10X magnification and the degree of vacuolar transformation was scored from 1 to 4, as described9 (ie, 1 = no vacuolation; 2 = ≥ 25% of hepatocytes vacuolated; 3 = 26% to 50% of hepatocytes vacuolated; and 4 = ≥ 51% of hepatocytes vacuolated). Cases were included in the study only if the degree of vacuolar transformation was scored as 3 or 4.
Procedures
Data retrieval—Medical records of cases included in the study were retrieved, and information on signalment and results of clinicopathologic testing, including CBC, serum biochemical profile, and urinalysis results, and diagnostic tests confirming a definitive diagnosis were recorded. Medical records were scrutinized for any indication that the dog had been treated with any glucocorticoid-containing drugs, whether by the parenteral, oral, topical, or ophthalmic route, and for any indication of assessments for HAC.
Control selection—For comparison purposes, a control population was assembled from all dogs ≥ 2 years old examined at the Cornell University Hospital for Animals during 1993, 1997, or 2001, and information on age, sex, and reproductive status was obtained. The control population was limited to dogs ≥ 2 years old to reduce bias introduced by inclusion of young healthy dogs brought to the hospital for vaccination or routine neutering.
Clinicopathologic testing—For dogs included in the study, CBCs had been performed with an automated instrumenta calibrated for canine cells that calculated Hct, hemoglobin concentration, RBC count, WBC count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and RBC distribution width. Differential cell counts and cell morphology had been determined manually. Serum biochemical profiles had also been performed with an automated instrumentb that calculated total protein, albumin, sodium, potassium, chloride, calcium, phosphorus, magnesium, bicarbonate, glucose, cholesterol, urea nitrogen, creatinine, and total bilirubin concentrations and ALP, GGT, alanine aminotransferase, aspartate aminotransferase, amylase, lipase, and creatine kinase activities. Urinalysis included determination of specific gravity and routine dipstick and sediment evaluations. Serum bile acid concentrations were determined after food had been withheld a minimum of 12 hours and again 2 hours after feeding by use of a linked enzymatic reaction, with the highest bile acid concentration for paired samples used for statistical comparisons.25,26 Chemiluminescence proceduresc were used for tests of thyroid function, adrenal gland function, and ACTH concentration. Serum sex hormone concentrations were measured by means of radioimmunoassay procedures validated for use in dogs.27
Disease categorization—Dogs were grouped on the basis of underlying disorder. Disease groups that were considered included neoplastic disease, acquired hepatobiliary disease, adrenal gland dysfunction, neurologic disease, immune-mediated disease, gastrointestinal tract disease, portosystemic vascular anomaly, renal disease, infectious disease, cardiac disease, diabetes mellitus, and miscellaneous disorders. A diagnosis of neoplastic disease was made on the basis of results of histologic examination of biopsy specimens. A diagnosis of acquired hepatobiliary disease was made on the basis of results of histologic review of hepatic biopsy specimens. A diagnosis of adrenal gland dysfunction was made on the basis of results of an ACTH response test, low-dose dexamethasone suppression test, or abdominal ultrasonography. In particular, a diagnosis of hypoadrenocorticism was made on the basis of a subnormal increase in serum cortisol concentration after administration of ACTH, and a diagnosis of HAC was made on the basis of an exaggerated increase in serum cortisol concentration after administration of ACTH or inadequate suppression of serum cortisol concentration 8 hours after administration of a low dose of dexamethasone (0.015 mg/kg [0.007 mg/lb], IV) in dogs with characteristic features of HAC. Adrenal hyperplasia was differentiated from neoplasia on the basis of results of ultrasonographic imaging and, in some cases, endogenous plasma ACTH concentration. Some dogs with classic signs and necropsy evidence of HAC were classified as having adrenal gland dysfunction associated with steroidogenic hormones. Dogs with adrenal masses that were histologically confirmed to be pheochromocytomas were included in the neoplasia group rather than the adrenal gland dysfunction group. Neurologic diseases were diagnosed on the basis of results of a neurologic examination in combination with radiography, computed tomography, and magnetic resonance imaging. In some instances, CSF analysis and histologic examination of muscle and nerve biopsy specimens were used to help identify specific neurologic diseases. The immune-mediated disease group included diseases affecting various organ systems. For these dogs, the diagnosis was made on the basis of results of physical examination and clinicopathologic testing, including specific immune function testing. Gastrointestinal tract disease was identified on the basis of results of histologic examination of endoscopically or surgically obtained biopsy specimens in conjunction with results of diagnostic imaging and clinicopathologic testing. Portosystemic vascular anomalies were confirmed by means of color-flow Doppler ultrasonography, colorectal scintigraphy, and histologic examination of hepatic biopsy specimens. A diagnosis of renal disease was made on the basis of histologic examination of renal biopsy specimens or sequential clinicopathologic data indicative of impaired renal function. A diagnosis of cardiac disease was made on the basis of history and physical examination findings in conjunction with results of electrocardiography, radiography, and echocardiography. A diagnosis of infectious disease was made on the basis of positive bacterial or fungal culture results or seroconversion to a specific infectious organism that reconciled with clinical signs and clinicopathologic test results. A diagnosis of diabetes mellitus was made on the basis of characteristic historical and clinicopathologic findings.
All dogs were further stratified according to their exposure to exogenous or excess endogenous glucocorticoids. All dogs with adrenal gland dysfunctions associated with steroidogenic hormone excess were characterized as having been exposed to glucocorticoids. Dogs with hypoadrenocorticism were classified as having been exposed to glucocorticoids because of treatments they received. Dogs with adrenal gland masses that lacked clinical or clinicopathologic features consistent with HAC were characterized as having not been exposed to glucocorticoids.
Histologic evaluation of hepatic lesions—Acinar zonal distribution of hepatocyte vacuolation was determined by means of histologic examination of biopsy specimens and assigned a score from 1 to 6. A score of 1 represented periportal vacuolar changes localized to zone 1; a score of 2 represented midzonal vacuolar changes localized to zone 2; a score of 3 represented perivenular (periacinar) vacuolar changes localized to zone 3; a score of 4 represented diffuse vacuolar changes involving all zones; a score of 5 represented vacuolar changes involving zones 1 and 2; and a score of 6 represented vacuolar changes involving zones 2 and 3.
Severity of hepatocellular vacuolation was categorized as moderate or severe. Dogs with diffuse vacuolation were categorized as having severe VH, as were dogs with involvement of 2 zones that also had histologic evidence of stromal collapse (ie, dropout of degenerating hepatocytes resulting in distortion of the hepatic sinusoids).
Statistical analysis—Age and weight distributions of dogs included in the study and distributions of scores for acinar distribution and severity of hepatocyte vacuolation were examined by use of box-and-whisker plots and histograms to determine whether data were normally distributed. Subsequently, nonparametric methods were used to detect significant differences between disease categories, severity groups, and acinar distribution groups. Data are given as median and range. The Wilcoxon rank sum test was used to test for significant differences between disease groups, between dogs with severe versus moderate VH, and between dogs with and without exposure to glucocorticoids (with and without inclusion of dogs in the adrenal gland dysfunction group). Contingency tables were used to detect significant differences in sex and reproductive status distributions between dogs with VH and control dogs. Contingency tables were also used to detect significant differences in vacuolation severity scores and zonal vacuolar distribution scores between dogs with and without exposure to glucocorticoids (with and without inclusion of dogs in the adrenal gland dysfunction group). Taking into consideration the multiple comparisons performed, we applied a Bonferroni-like correction to a P value cutoff of 0.05. Thus, for data analyzed by use of contingency tables, values of P < 0.01 were considered significant, and for data analyzed by use of the Wilcoxon rank sum test, values of P < 0.001 were considered significant. All analyses were performed with standard software.d
Results
A total of 336 cases met the criteria for inclusion in the study. For 165 of the 336 cases, liver tissue had been collected at the time of necropsy. For the remaining cases, liver tissue had been collected by means of surgical biopsy or laparoscopy-assisted biopsy.
Median age of dogs with VH (9 years; range, 1 to 19 years) was significantly (P < 0.001) greater than median age of control dogs (6 years; range, 2 to 27 years). Compared with the control group of dogs, there were significantly (P < 0.001) fewer dogs with VH that were ≤ 3 years old and significantly (P < 0.001) more dogs with VH that were between 11 and 14 years old. Most dogs with VH that were ≤ 11 years old were classified in the neoplastic disease, acquired hepatobiliary disease, adrenal gland dysfunction, or neurologic disease groups. The proportion of neutered females was significantly (P = 0.009) higher among dogs with VH (157/323 [49%]) than among control dogs (5,492/13,266 [41%]), and the proportion of neutered males was significantly (P = 0.001) lower among dogs with VH (80/323 [25%]) than among control dogs (4,546/13,266 [34%]). Of liver samples collected at the time of necropsy (165/336 [49%]), 33% were from dogs with neoplastic disease, 21% were from dogs with neurologic disease, 11% were from dogs with immunemediated disease, and the remainder were from dogs with other disorders.
Overall, 94 of the 336 dogs were assigned to the neoplastic disease group, 43 were assigned to the acquired hepatobiliary disease group, and 40 were assigned to the adrenal gland dysfunction group (Table 1). The 17 dogs assigned to the miscellaneous disorders group (including disorders in which ≤ 2 dogs were represented) included dogs with zinc toxicosis, ethylene glycol toxicosis, myositis, interstitial pneumonia, an arytenoid mass, laryngeal paralysis, chronic pyogranulomatous dermatitis, chronic prostatitis, steatitis, esophageal stricture, megaesophagus, systemic amyloidosis, splenic infarction, pulmonary histocytosis, and unexplained aggressive behavior.
Underlying diseases identified in dogs with VH.
| Underlying disease | No. of dogs | Percentage |
|---|---|---|
| Renal disease | 12 | 3.6 |
| Chronic renal disease | 7 | 2.1 |
| Glomerulonephritis | 2 | 0.6 |
| Other | 3 | 0.9 |
| Immune-mediated disease | 34 | 10.1 |
| Hemolytic anemia | 12 | 3.6 |
| Thrombocytopenia | 6 | 1.8 |
| Hemolytic anemia and thrombocytopenia | 6 | 1.8 |
| Systemic lupus erythematosus | 4 | 1.2 |
| Other | 6 | 1.8 |
| Cardiac disease | 5 | 1.5 |
| Congestive heart failure | 3 | 0.9 |
| Other | 2 | 0.6 |
| Acquired hepatobiliary disease | 43 | 12.8 |
| Chronic hepatitis, cirrhosis, or liver failure | 11 | 3.3 |
| Cholangiohepatitis or cholangitis | 8 | 2.4 |
| Hepatotoxicosis | 5 | 1.5 |
| Hepatic fibrosis | 4 | 1.2 |
| Cholecystitis | 4 | 1.2 |
| Extrahepatic bile duct obstruction | 3 | 0.9 |
| Hepatocutaneous syndrome | 3 | 0.9 |
| Acute liver failure | 3 | 0.9 |
| Other | 2 | 0.6 |
| Adrenal gland dysfunction | 40 | 11.9 |
| Pituitary-dependent HAC | 21 | 6.3 |
| Adrenal neoplasia | 14 | 4.2 |
| Sex hormone adrenal hyperplasia | 3 | 0.9 |
| Other | 2 | 0.6 |
| Neoplasia | 94 | 28.0 |
| Lymphosarcoma | 19 | 5.7 |
| Adenocarcinoma | 15 | 4.5 |
| Hemangiosarcoma | 13 | 3.9 |
| Meningioma | 5 | 1.5 |
| Leukemia | 4 | 1.2 |
| Multiple tumors | 4 | 1.2 |
| Hepatoma | 4 | 1.2 |
| Transitional cell carcinoma | 3 | 0.9 |
| Osteosarcoma | 3 | 0.9 |
| Hepatocellular carcinoma | 3 | 0.9 |
| Pheochromocytoma | 3 | 0.9 |
| Other | 18 | 5.4 |
| Neurologic disease | 38 | 11.3 |
| Intervertebral disk disease | 7 | 2.1 |
| Degenerative myelopathy | 8 | 2.4 |
| Wobbler syndrome | 3 | 0.9 |
| Peripheral neuropathy | 3 | 0.9 |
| Other | 17 | 5.1 |
| Gastrointestinal tract disease | 31 | 9.2 |
| Inflammatory bowel disease | 12 | 3.6 |
| Pancreatitis | 8 | 2.4 |
| Pancreatitis and inflammatory bowel disease | 3 | 0.9 |
| Peritonitis | 3 | 0.9 |
| Other | 5 | 1.5 |
| Portosystemic vascular anomaly | 13 | 3.9 |
| Infectious disease | 6 | 1.8 |
| Diabetes mellitus | 3 | 0.9 |
| Miscellaneous | 17 | 5.1 |
| Total | 336 | 100.0 |
Of the 336 dogs with VH, 186 (55%) were classified as having been exposed to glucocorticoids (ie, exogenous glucocorticoid administration or high endogenous glucocorticoid or steroidogenic hormone concentrations) and 150 (45%) were classified as not having been exposed to glucocorticoids (Table 2). Median age of dogs exposed to glucocorticoids (8.5 years; range, 1 to 16 years) was not significantly (P = 0.6) different from the median age of dogs not exposed to glucocorticoids (8.7 years; range, 1 to 19 years). Similarly, median body weight of dogs exposed to glucocorticoids (24.1 kg [53 lb]; range, 3.2 to 78 kg [7 to 172 lb]) was not significantly (P = 0.6) different from median body weight of dogs not exposed (21.0 kg [46.2 lb]; range, 2.2 to 62 kg [4.8 to 136.4 lb]). Differences were not found between groups when dogs with adrenal gland dysfunction were excluded from analyses.
Numbers of dogs with VH, grouped on the basis of underlying disease, that did or did not have evidence of overt exposure to glucocorticoids (ie, exogenous glucocorticoid administration or high endogenous glucocorticoid concentration).
| Disease category | All dogs | Moderate VH | Severe VH | |||
|---|---|---|---|---|---|---|
| Glu+ | Glu− | Glu+ | Glu− | Glu+ | Glu− | |
| Neoplastic disease | 50 (27) | 44 (29) | 15 (26) | 27 (31) | 35 (27) | 17 (27) |
| Acquired hepatobiliary disease | 7 (4) | 36 (24) | 3 (5) | 20 (23) | 4 (3) | 16 (25) |
| Adrenal gland dysfunction | 32 (17) | 8 (5) | 8 (14) | 2 (2) | 24 (19) | 6 (9) |
| Neurologic disease | 31 (17) | 7 (5) | 11 (19) | 3 (3) | 20 (16) | 4 (6) |
| Immune-mediated disease | 30 (16) | 4 (3) | 10 (18) | 1 (1) | 20 (16) | 3 (5) |
| Gastrointestinal tract disease | 16 (9) | 15 (10) | 6 (11) | 7 (8) | 10 (8) | 8 (13) |
| Portosystemic vascular anomaly | 1 (0.5) | 12 (8) | 0 (0) | 9 (10) | 1 (1) | 3 (5) |
| Renal disease | 6 (3) | 6 (4) | 2 (4) | 5 (6) | 4 (3) | 1 (2) |
| Infectious disease | 3 (2) | 3 (2) | 0 (0) | 2 (2) | 3 (2) | 1 (2) |
| Cardiac disease | 0 (0) | 5 (3) | 0 (0) | 4 (5) | 0 (0) | 1 (2) |
| Diabetes mellitus | 0 (0) | 3 (2) | 0 (0) | 2 (2) | 0 (0) | 1 (2) |
| Miscellaneous disorders | 10 (5) | 7 (5) | 2 (4) | 4 (5) | 8 (6) | 3 (5) |
| Total | 185 (55) | 150 (44) | 57 (40) | 86 (60) | 129 (67) | 64 (33) |
Data are given as number of dogs (%).
Glu+ = Evidence of overt exposure to glucocorticoids. Glu− = No evidence of overt exposure to glucocorticoids.
Of the 336 dogs, 193 had severe VH, of which 129 had been exposed to glucocorticoids and 64 had not been, and 143 had moderate VH, of which 57 had been exposed to glucocorticoids and 86 had not been. For dogs with severe VH, the proportion that had been exposed to glucocorticoids was significantly (P < 0.001) higher than the proportion that had not been (Table 2), regardless of whether dogs with adrenal gland dysfunction were or were not included in the analysis. Dogs that had been exposed to glucocorticoids were 3 times as likely (95% confidence interval, 1.9 to 4.8) to have severe VH as were dogs that had not been exposed, when all dogs were considered, and 3.1 times as likely (95% confidence interval, 1.9 to 5.0) to have severe VH as were dogs that had not been exposed when dogs with adrenal gland dysfunction were excluded.
Overall, 155 of the 336 (46%) dogs were assigned an acinar zonal distribution score of 4 (ie, diffuse vacuolar changes involving all zones), 81 (24%) were assigned a score of 2 (ie, midzonal vacuolar changes localized to zone 2), 77 (23%) were assigned a score of 6 (ie, vacuolar changes involving zones 2 and 3), 18 (5%) were assigned a score of 3 (ie, perivenular vacuolar changes localized to zone 3), 3 (0.9%) were assigned a score of 5 (ie, vacuolar changes involving zones 1 and 2), and only 2 (0.6%) were assigned a score of 1 (ie, periportal vacuolar changes localized to zone 1). Distribution of acinar zonal distribution scores was not significantly different between dogs that had or had not been exposed to glucocorticoids, regardless of whether dogs with adrenal gland dysfunction were or were not included in the analysis.
Nine dogs with severe VH associated with overproduction of endogenous steroidogenic hormones or chronic administration of glucocorticoids at high dosages developed compromised hepatic function characterized by biochemical evidence of cholestasis, parenchymal stromal collapse, and formation of regenerative nodules. Four of these dogs died. Seven dogs with severe VH underwent cholecystectomy because of biliary mucoceles.
Clinicopathologic features—There were no significant differences in clinicopathologic variables between dogs that had been exposed to glucocorticoids and dogs that had not been exposed, regardless of whether dogs with adrenal gland dysfunction were or were not included in analyses. Overall, 226 of the 336 (67%) dogs had high ALP activity, of which 124 (55%) had been exposed to glucocorticoids and 102 (45%) had not. Similarly, there were no significant differences in clinicopathologic variables between dogs with severe VH and dogs with moderate VH, regardless of whether dogs with adrenal gland dysfunction were or were not included in analyses.
Discussion
In dogs, VH is commonly associated with glucocorticoid administration or HAC and with high ALP activity. However, in the present study, we found that 45% of dogs with moderate or severe VH had no evidence of overt glucocorticoid exposure. Thus, our findings support the hypothesis that stress-induced hypercortisolemia associated with acute or chronic illness may contribute to the development of VH in dogs. Similarly, previous studies19–22 have found exaggerated increases in serum cortisol concentrations in response to administration of ACTH, high urine cortisol-to-creatinine concentration ratios, and high glucocorticoidALP isoenzyme activity in many dogs with nonadrenal gland disorders. Endogenous stress or disease-related glucocorticoid release may initiate development of VH (hepatocyte glycogen retention) through the interaction of glucocorticoid with transcriptionally responsive genes.28–30 Thus, a diagnosis of VH should initiate a diagnostic search for a primary disease process if exogenous glucocorticoid administration and HAC are ruled out.
We also found in the present study that 45% of dogs with high serum ALP activity did not have any evidence of overt glucocorticoid exposure, and the wide overlap in values for serum ALP activity between dogs with and without overt glucocorticoid exposure made it impossible to differentiate whether any individual dog did or did not have glucocorticoid exposure on the basis of ALP activity alone. It is possible that incomplete extraction of historical information regarding glucocorticoid treatment complicated our findings. Even though we suspected that dogs without documented glucocorticoid exposure had physiologic stress as a result of the underlying primary disease process23,24,31,32 the retrospective nature of this study made it impossible to investigate endogenous concentrations of glucocorticoids or other steroidogenic hormones in these individuals. The long-recognized association between exposure to glucocorticoids and VH in dogs has led to the common perception that HAC is typically the underlying cause, but findings of the present study clearly illustrate that this assumption is erroneous. Only 40 of the 336 (11.9%) dogs in the present study had adrenal gland dysfunction, including pituitary-dependent HAC, atypical HAC (ie, HAC associated with high 17-α-hydroxyprogesterone concentrations), and adrenocortical neoplasia, and we were unable to differentiate etiopathologic mechanisms of VH on the basis of clinicopathologic features, including hepatic enzyme activity.
In the present study, 94 of the 336 (28%) dogs had neoplasia, and 44 of these 94 (47%) dogs had no evidence of overt glucocorticoid exposure. Similarly, a previous study22 of dogs with lymphoma found that increased glucocorticoid-ALP isoenzyme occurred in more than 80% of dogs with high ALP activity that had not been given exogenous glucocorticoids. Other studies have documented high urine cortisol-to-creatinine concentrations ratios in dogs with lymphosarcoma21 and abnormal adrenal function test results in dogs with lymphoma or nonhematopoietic neoplasia.32 However, caution is warranted when interpreting our finding that VH was most often affiliated with neoplasia, because the diagnosis of VH was made on the basis of histologic examination of samples obtained during surgery or necropsy. Fifty-four of the 165 (33%) dogs in which VH was diagnosed at necropsy had neoplasia, yet the prevalence of neoplasia in all dogs necropsied in our hospital during the study period could not be determined. It is important to acknowledge that dogs with VH associated with neoplasia may have had chronic or advanced disease, increasing the likelihood of a stress response and secondary induction of VH as well as the likelihood that tissues would be obtained at necropsy for examination. Although high hepatic enzyme activity may reflect primary hepatic or metastatic neoplasia, our findings confirm that VH and accompanying high hepatic enzyme activity may be found in individuals with nonhepatic neoplasia, as has been reported previously.33 High endogenous glucocorticoid concentrations secondary to stress and production of steroidogenic hormones other than cortisol could explain the development of VH in some dogs with nonadrenal neoplasia.32
An unexpectedly high proportion of dogs in the present study had congenital or acquired hepatobiliary disorders. Especially surprising was the association between portosystemic vascular anomalies and VH. High cortisol concentrations have been proposed to influence physiologic responses and pituitary function in dogs with acquired and congenital portosystemic vascular shunts.34,35 However, further study is needed to elucidate whether this accounts for the association between VH and portosystemic vascular anomalies. Dogs with acquired liver disease had primary necrotic or inflammatory disorders in the present study. Regardless of the etiopathogenesis of VH in these dogs, the association is an important finding and emphasizes that caution should be used in interpreting results of histologic examination of small needle biopsy specimens or cytologic examination of aspirates in dogs suspected to have hepatic disease.36–38
Although most dogs in the present study were examined because of the primary disorder, in some dogs, diagnostic testing was pursued because of high serum ALP activity. In dogs, glucocorticoid administration most often results in increases in serum ALP and GGT activities and, to a lesser extent, serum alanine aminotransferase and aspartate aminotransferase activities.2,3,5,8–10,39–42 In the present study, for both dogs with and without evidence of overt glucocorticoid exposure, median serum ALP activity was 4 to 5 times the upper reference limit. It is well established that serum ALP activity is a nonspecific indicator of disease in dogs because ALP is produced in multiple body sites and has multiple isoenzymes.30
Other investigations have confirmed an association between increases in glucocorticoid-ALP activity and a variety of nonadrenal disorders, including diabetes mellitus, hypothyroidism, hepatic disease, and other chronic illnesses.17–19,22 Because of this, glucocorticoid-ALP activity cannot be used as a reliable diagnostic indicator of primary adrenal disease. Because glucocorticoid-ALP activity was not routinely measured in dogs in the present study, we were unable to determine whether there was an association between VH and glucocorticoid-ALP activity.
Acinar zonal distribution of vacuolation was variable in the present study, although a diffuse or predominantly zone 2 or 3 distribution prevailed. Similarly, in dogs in which glucocorticoid administration has been used to experimentally induce VH, variable patterns of zonal involvement have been identified; however, with chronic glucocorticoid administration, a diffuse distribution is most common.1,2,5,6,9 In the present study, 280 of the 336 (83%) dogs had a condition assigned to 1 of 6 disease categories (neoplastic disease, acquired hepatobiliary disease, adrenal gland dysfunction, neurologic disease, immune-mediated disease, and gastrointestinal tract disease), and of these, 167 (60%) had a severe VH. Although severe VH was more common in dogs exposed to glucocorticoids (129/186 [69%]), a substantial number of dogs without any evidence of overt glucocorticoid exposure (64/150 [43%]) also had severe VH.
Dogs in the present study with VH were significantly older than control dogs. This was not unexpected, in that older dogs would be more likely to have a higher prevalence of chronic conditions capable of causing physiologic stress. We also found a significantly higher proportion of neutered females and a significantly lower proportion of neutered males among dogs with VH, compared with the control group, suggesting that an androgenic effect might have been contributing to the development of VH. However, further study is required to investigate this possibility.
Finally, findings of the present study suggest that VH should not be considered a nonprogressive or unimportant lesion. Nine dogs in this study developed overt hepatic dysfunction secondary to severe VH, and 4 of these dogs died. Furthermore, there appeared to be an association between severe VH and biliary mucocele.
ABBREVIATIONS
| VH | Vacuolar hepatopathy |
| ALP | Alkaline phosphatase |
| GGT | γ-Glutamyltransferase |
| HAC | Hyperadrenocorticism |
Coulter S+ IV electronic counter, Coulter Electronics, Hialeah, Fla.
Hitachi 911, Boehringer Mannheim, Indianapolis, Ind.
Thyroid, cortisol, and ACTH assays, Immulite, Diagnostic Products Corp, Los Angeles, Calif.
Statistix, version 7.0, Analytical Software, Tallahassee, Fla.
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