CASE REPORT
Hypokalaemic paresis, hypertension, alkalosis and adrenal-dependent hyperadrenocorticism in a dog
DR DAVIES,ª SF FOSTER, BJ HOPPER, KL STAUDTE, AJ O’HARA and PJ IRWIN
Generalised paresis, severe hypokalaemia and kaliuresis, metabolic alkalosis and hypertension, characteristic of mineralocorticoid excess, were identified in a dog with hyper- adrenocorticism due to a functional adrenocortical carcinoma. Aldosterone concentration was decreased and deoxycorti- costerone concentration increased in the presence of hypo- kalaemia. These metabolic abnormalities resolved with resec- tion of the carcinoma. Mineralocorticoid excess in dogs with hyperadrenocorticism is generally considered to be of little clinical significance but resulted in the acute presentation of this patient. The possible pathogenesis of mineralocorticoid excess in this case of canine hyperadrenocorticism is discussed. Aust Vet J 2008;86:139-146 doi: 10.1111/j.1751-0813.2008.00276.x
| 11-ß-HSD-2 | 11-B-hydroxysteroid dehydrogenase-2 |
| ACTH | Adrenocorticotropic hormone |
| ADH | Adrenal-dependent hyperadrenocorticism |
| DOC | 11-deoxycorticosterone |
| HAC | Hyperadrenocorticism |
| KTZ | Ketoconazole |
| PDH | Pituitary-dependent hyperadrenocorticism |
H yperadrenocorticism (HAC) is a common endocri- nopathy of middle-aged to older dogs and approximately 15 to 20% of these dogs have adrenal- dependent hyperadrenocorticism (ADH) with excessive production of cortisol from autonomously secreting adrenocortical tumours.1 The constellation of clinical and laboratory findings that occurs in canine HAC1 (canine Cushing’s syndrome) is well known to veterinary practitioners. Hypokalaemia and metabolic alkalosis are generally considered to be of little clinical significance in canine HAC.1 This is in contrast to the disease in humans, where some patients can develop severe and life- threatening hypokalaemia.2 This case report describes severe hypokalaemia, paresis, systolic hypertension and alkalosis in a dog with HAC due to a functional adrenocortical carcinoma. These abnormalities resolved following surgical resection of the
mass. The possible pathogenesis of these abnormalities, typical of mineralocorticoid excess, is discussed.
Case report
A 10-year-old desexed female Maltese-Australian Silky Terrier cross presented to Murdoch University Veterinary Hospital for assessment of complications arising during treatment of HAC. HAC had been diagnosed one month previously with clinical signs of polyuria, polydipsia, polyphagia, abdominomegaly and cutaneous bruising, laboratory findings of increased alkaline phosphatase and alanine aminotransferase activity and supportive low-dose dexamethasone suppression test results (0-hour cortisol 147 nmol/L, 4-hour cortisol 124 nmol/L, 8-hour cortisol 122 nmol/L). Plasma potassium concentration was normal at this time. Testing to differentiate pituitary-dependent hyperadrenocorticism (PDH) from ADH had not been performed prior to treatment with mitotane. An ACTH stimulation test performed 5 days prior to referral, after 15 days of mitotane at approximately 50 mg/kg/day, showed a post- stimulation cortisol concentration of 241 nmol/L, indicating inadequate control of HAC.3 Three days later, a gait abnormality with paresis developed. There was no improvement with cage rest and administration of prednisolone (5 mg orally) and carprofen (dose unknown) and the dog was referred for neurological assessment.
Physical examination revealed a sparse hair coat with epidermal crusts (typical of superficial pyoderma), abdominomegaly and tachypnoea. The dog had a markedly abnormal gait, with generalised weakness and a shortened limb action. It was unable to walk for more than a few metres at a time and was unable to elevate its head. Neurological examination revealed no abnormalities in cranial nerves, spinal reflexes or nociception. Repeated Doppler sphygmomanometry was indicative of systolic hypertension, at 180 to 220 mmHg.4
Results of initial haematological examination, serum biochemical analysis, urinalysis and urine culture are presented in Table 1 and electrolytes and blood gas analysis in Table 2. Changes consistent with HAC were present, with marked increases in hepatic enzyme activities, marked hypokalemia and a mild increase in creatine kinase also noted. Blood gas analysis showed metabolic
SMALL ANIMALS
| Parameter | Patient Value | Reference Range |
|---|---|---|
| Haematology | ||
| Haemoglobin (g/L) | 190 | 120-180 |
| Packed cell volume (L/L) | 0.55 | 0.37-0.55 |
| Red blood cells (x 1012/L) | 8.1 | 5.5-8.5 |
| Mean corpuscular haemoglobin | 341 | 320-360 |
| concentration (g/L) | ||
| Mean corpuscular haemoglobin (pg) | 23 | 20-25 |
| Mean corpuscular volume (fL) | 69 | 60-70 |
| Total white blood cells (x109/L) | 17.6 | 6.0-17.0 |
| Neutrophils (x109/L) | 14.08 | 3.0-11.5 |
| Band neutrophils (x109/L) | 0.0 | 0.0-0.3 |
| Lymphocytes (x109/L) | 1.41 | 1.0-4.8 |
| Monocytes (x109/L) | 1.76 | 0.15-1.35 |
| Eosinophils (x109/L) | 0.35 | 0.15-1.25 |
| Platelets (×1012/L) | Normal | 200-900 |
| Prothrombin time (sec) | 6 | <12 |
| Activated partial thromboplastin time (sec) | 12 | <24 |
| Serum biochemistry | ||
| Creatine kinase (U/L) | 1230 | 47-228 |
| Aspartate aminotransferase (U/L) | 207 | 10-60 |
| Alanine aminotransferase (U/L) | 2092 | 21-142 |
| Alkaline phosphatase (U/L) | 10980 | 20-184 |
| Gamma glutamyl transferase (U/L) | 157 | 1-8 |
| Total bilirubin (umol/L) | 5 | 2-17 |
| Urea (mmol/L) | 3.5 | 3.6-10.0 |
| Creatinine (umol/L) | 62 | 44-132 |
| Lipase (U/L) | 926 | 0-500 |
| Amylase (U/L) | 1786 | 750-3000 |
| Glucose (mmol/L) | 5.6 | 3.6-6.8 |
| Cholesterol (mmol/L) | 15.1 | 3.3-6.9 |
| Total protein (g/L) | 61 | 56-80 |
| Albumin (g/L) | 30 | 24-38 |
| Globulin (g/L) | 31 | 28-44 |
| Calcium (mmol/L) | 2.42 | 2.20-2.80 |
| Phosphate (mmol/L) | 1.80 | 0.80-2.20 |
| Urine | ||
| Specific gravity | 1.005 | 1.001-1.070 |
| pH | 7.0 | variable |
| Protein | negative | negative to trace |
| Glucose | negative | negative |
| Ketones | negative | negative |
| Blood | negative | negative |
| Leukocytes (per high-power field) | 3 | 0-1 |
| Red blood cells (per high-power field) | 4 | 0-3 |
| Protein:creatinine ratio | 0.56 | <0.5 |
| Bacterial culture | negative |
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alkalosis with inadequate respiratory compensation, consistent with concurrent respiratory alkalosis. Arterial blood partial pressure of oxygen was normal (90 mmHg). No significant abnormalities were detected on thoracic radiographs. Abdominal ultrasound examination revealed a 2.2 x 2.2 × 1.7 cm mass in the right adrenal gland. The mass contained a central region of mineralisation that cast an irregular acoustic shadow, but was otherwise uniform (Figure 1). The left adrenal gland was normal, measuring 13.0 x 5.1 × 4.1 mm. The liver was enlarged and diffusely increased in echogenicity. Differential diagnoses at this time included ADH, adrenal neoplasia with autonomous mineralocorticoid or sex steroid production and PDH with concurrent functional or non-functional adrenal mass (carcinoma, adenoma, phaeochro- mocytoma, granuloma, metastatic neoplasia). Initial therapy comprised oral potassium gluconate (4 mEq orally twice daily) for hypokalaemia, enalapril (0.3 mg/kg orally once daily) for hypertension and cephalexin (9 mg/kg orally twice daily) for pyoderma and possible urinary tract infection (pending urine culture results). Moderate improvement in paresis was noted over the next 48 hours. Hypertension persisted and prompted a change from enalapril to prazosin (0.06 mg/kg orally twice daily) on Day 4, with a decrease in systolic blood pressure to 130 to 180 mmHg observed over the next 2 days (Table 2).
On Day 4 there was an acute worsening of paresis, with palpably firm muscles that did not ‘dimple’ when percussed, as may be seen in myotonia. Plasma electrolyte analysis showed worsening hypokalaemia (2.0 mmol/L). Intravenous potassium chloride infusion was instituted (0.2 mmol/kg/h), with partial correction of hypokalaemia and improvement in paresis observed (Table 2).
| Day | 1 | 3 | 4 | 6 | 10 | 20 | 33 | 34 | 46 | 47 pre-op | Reference range |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Electrolytes (mmol/L): | |||||||||||
| Sodium | 147 | 150 | 146-151 | 151 | 151 | 153 | 146 | 146 | 149 | 151 | 139-154ª |
| Potassium | 2.4 | 2.7 | 2.0-2.5 | 2.9 | 2.6 | 2.9 | 3.9 | 3.4 | 2.7 | 2.9 | 3.4-5.3ª |
| Chloride | 102 | 111 | 112-116 | 110 | 116 | 113 | 110 | 109 | 111 | 111 | 99-120ª |
| Venous blood gases: | |||||||||||
| pH | 7.47 | 7.42 | 7.31-7.40ª | ||||||||
| pCO2 (mmHg) | 37 | 42 | 33.0-50.0ª | ||||||||
| HCO3- (mmol/L) | 26 | 26 | 18.1-26.1ª | ||||||||
| TCO2 (mmol/L) | 27 | 27 | 19.1-27.6ª | ||||||||
| Base excess (mmol/L) | +4 | +2 | -5.4-+1.2ª | ||||||||
| Fractional excretion of potassium (%) | 45 | < 6%b | |||||||||
| Systolic blood pressure (mmHg) | 180-220 | 190 | 180-220 | 140-180 | 165 | 120-180 | < 160℃ | ||||
| Cortisol (nmol/L) | |||||||||||
| Resting | 95 | 25-75ª | |||||||||
| 1-hour post-ACTH | 275 | 25-75ª | |||||||||
| Aldosterone (pmol/L): | |||||||||||
| Resting | < 70 | < 70 | 14-957ª | ||||||||
| 1-hour post-ACTH | 131 | 197-2103ª | |||||||||
| Deoxycorticosterone (nmol/L) | 4.0 | 1.92 ± 0.89f |
Treatment9
Enalapril
Prazosin
Spironolactone
Potassium gluconate
Potassium gluconate
Cephalexin
KCl IV
Fentanyl TD
Comments
Marked paresis
Marked paresis
Ketoconazole commenced Day 20. Medications stopped Day 31 due to vomiting
Increased ALT, AST, bilirubin
Liver biopsy
Right adrenalectomy
| Day | 47 post-op | 48 | 51 | 52 | 54 | 80 | 117 | 213 | 640 | Reference range |
|---|---|---|---|---|---|---|---|---|---|---|
| Electrolytes (mmol/L): | ||||||||||
| Sodium | 174 | 149-155 | 145 | 144-146 | 147 | 146 | 149 | 147 | 146 | 139-154ª |
| Potassium | 2.2 | 2.9-3.6 | 4.5 | 4.8-5.8 | 3.4 | 4.7 | 4.8 | 5.2 | 3.6 | 3.4-5.3ª |
| Chloride | 139 | 117-123 | 109 | 110 | 112 | 117 | 117 | 115 | 118 | 99-120ª |
| Venous blood gases: | ||||||||||
| pH | 7.36 | 7.36 | 7.43 | 7.31-7.40ª | ||||||
| pCO2 (mmHg) | 35 | 32 | 40 | 33.0-50.0ª | ||||||
| HCO3- (mmol/L) | 19 | 18 | 26 | 18.1-26.1ª | ||||||
| TCO2 (mmol/L) | 21 | 19 | 28 | 19.1-27.6ª | ||||||
| Base excess (mmol/L) | -5 | -6 | +2 | -5.4-+1.2ª | ||||||
| Fractional excretion of potassium (%) | < 6b | |||||||||
| Systolic blood pressure (mmHg) | 96-113 | 104-127 | 116 | 158-178 | < 160℃ | |||||
| Cortisol (nmol/L): | ||||||||||
| Resting | 41 | 14 | 27 | 235 | 25-75h | |||||
| 1-hour post-ACTH | 45 | 122 | 189 | 325 | 200-400h |
| Table 2. Continued | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Day | 47 post-op | 48 | 51 | 52 | 54 | 80 | 117 | 213 | 640 Reference range |
| Aldosterone (pmol/L) | |||||||||
| Resting | 14-957ª | ||||||||
| 1-hour post-ACTH | 197-2103ª | ||||||||
| Deoxycorticosterone (nmol/L) | 1.92 ± 0.89 | ||||||||
| Treatment9 | HSS IV | ||||||||
| KCl IV | |||||||||
| Cephazolin IV | Amoxycillin | ||||||||
| Cortisone acetate | |||||||||
| Fentanyl TD | Potassium gluconate | ||||||||
| Methadone IM | BUP IM | ||||||||
| Comments | Pancreatitis | Discharged | LDDXM normal Day 215 | Pulmonary metastases, cardiac failure | |||||
| Abbreviations and footnotes | ACTH adrenocorticotropic | hormone | a Murdoch | University | Veterinary | Hospital laboratory reference range | |||
| ALT alanine aminotransferase | b when hypokalaemia present; see Reference 7 | ||||||||
| AST aspartate aminotransferase | succinate | c see Reference | 4 | ||||||
| HSS hydrocortisone sodium BUP buprenorphine IM intramuscular injection | d for medical control of hyperadrenocorticism (Coat-a-Count cortisol RIA, University Veterinary Centre, University of Sydney; see Reference 3) Michigan State University reference range for Coat-a-Count | ||||||||
| IV intravenous infusion | aldosterone | RIA | (http://www.animalhealth.msu.edu/Sections/ | ||||||
| KCl potassium chloride | mean + standard 9 all medications h for normal | Endocrinology/Reference_Ranges.pdf) deviation from six normal dogs; see text given per os unless indicated; see text for doses dogs (Coat-a Count cortisol RIA, University Veterinary of Sydney) | |||||||
| LDDXM low-dose dexamethasone suppression test RIA radioimmunoassay | |||||||||
| TD transdermal administration | Centre, University | ||||||||
The patient was discharged on Day 6 on oral spironolactone (1.6 mg/kg twice daily) and potassium gluconate (8 mEq twice daily) for management of presumed mineralocorticoid excess, pending pre- and post-adrenocorticotropic hormone (ACTH) aldosterone assaysª validated in dogs.5 These showed an undetectable resting aldosterone concentration, with subnormal response to ACTH (Table 2).
On Day 10, the dog was systemically well, with an improved gait. Hypokalaemia persisted (2.6 mmol/L) and urinary fractional excretion of potassium was inappropriately high (45%; Table 2). Ketonazole (KTZ) was commenced on Day 20 to provide temporary control of hypercortisolaemia prior to planned adrenalectomy, at an initial dose of 6.25 mg/kg orally twice daily. After 8 days without adverse effects the dose of KTZ was increased to 12.5 mg/kg twice daily. Vomiting and anorexia commenced the following day and lasted for 2 days; vomiting resolved but anorexia persisted despite withdrawal of all medications on Day 31. Serum biochemistry analysis on Day 33 showed marked increases in alanine aminotransferase (2660 U/L) and aspartate aminotrans- ferase (297 U/L) relative to alkaline phosphatase (483 U/L), with concurrent hyperbilirubinaemia (71.7 umol/L). Electrolyte concentrations were normal (Table 2). Cortisol concentration after ACTH stimulation (Day 34), using a previously validated assay, (Coat-a-Count cortisol radioimmunoassay, Diagnostic
Products)6 indicated inadequate conbrol of HAC (Table 2). Histopathological examination of hepatic needle biopsies showed a mild periportal infiltration of lymphocytes, neutrophils, eosi- nophils and histiocytic cells; parenchymal Ito cells were mildly increased and there was mild hepatocellular hydropic vacuolation and anisocytosis. KTZ-induced hepatotoxicity was suspected and clinical recovery from this episode was uneventful.
On Day 46 the patient was re-admitted in preparation for right adrenalectomy. Increases in water consumption and appetite had been noted since the previous visit. Blood gas and electrolyte analysis showed relapse of hypokalaemia and metabolic alkalosis with adequate respiratory compensation (Table 2). On the morning of surgery (Day 47), blood was collected and serum and heparinised plasma stored at -30℃ for further steroid assays. For the 11-deoxycorticosterone (DOC) assay, serum was extracted by diethyl-ether and purified by celite chromatography. DOC was then assayed by radioimmunoassay with a 3H-DOC tracer and anti-human DOC antibody (ICN Biomedicals Australasia). Aldosterone (Coat-a-Count aldosterone radioim- munoassay, Diagnostic Products) was again undetectable and DOC was 4.0 nmol/L. The DOC assays were also performed on samples submitted from six control dogs with normal electro- lytes; DOC concentrations ranged from 1.0 to 3.2 nmol/L (mean ± standard deviation 1.92 ± 0.89 nmol/L).
Prior to surgery an intravenous hydrocortisone sodium succinate infusion (0.7 mg/kg/h) and crystalloid fluid therapy (Hartmann’s solution) were commenced. The right adrenal gland mass was located via midline ventral laparotomy and was dissected from the adjacent caudal vena cava and right renal vein. Although there was no gross evidence of invasion, small remnants of adrenal capsule could not be resected due to an extensive network of vessels penetrating into the capsule, in close association with the caudal vena cava. There was no visible evidence of intra-abdominal metastasis. Intraoperative hypotension was corrected with an intravenous Dextran 70 bolus and intravenous dobutamine infusion. Severe hypokalaemia (2.2 mmol/L) was noted post- operatively and an intravenous infusion of potassium chloride (0.5 mmol/kg/hr) was commenced. Plasma potassium con- centration ranged from 2.8 to 3.6 mmol/L for 48 hours post- operatively and thereafter remained above the lower reference value of 3.4 mmol/L (Table 2). Histopathological examination of the excised adrenal gland revealed a disorderly proliferation of large foamy epithelial cells compressing the adjacent adrenal medullary tissue and invading the adrenal capsule (Figure 2). The epithelial cells were aggregated into sheets, nests and cords by a delicate fibrovascular stroma, disrupted by multifocal areas of necrosis, haemorrhage, mineralisation and acicular cleft formation (Figure 3). There was occasional arcuate and pseu- doacinar organisation and the neoplastic cells exhibited moderate anisocytosis. The histological diagnosis was adrenocortical carcinoma.
Five days postoperatively (Day 52) an ACTH stimulation testb was performed and showed minimal response (Table 2). An epi- sode of pancreatitis commenced later the same day but resolved within 48 hours with conservative management. Seven days after surgery (Day 54) plasma electrolyte concentrations were normal and the dog was discharged on oral cortisone acetate (1 mg/kg twice daily) for the management of post-adrenalectomy hypocortisolism. Amoxycillin (11.5 mg/kg orally three times
daily) was also administered, pending bacterial culture of an indwelling urinary catheter maintained perioperatively (subsequently negative). One month after surgery (Day 80) the dog showed good hair regrowth, decreased abdominal girth, normal water intake and no signs of weakness. An ACTH stimulation testb showed a mildly sub-normal post-stimulation cortisol con- centration (Table 2) and cortisone acetate was discontinued. Two months after surgery (Day 117) there was continued clinical improvement and a normal gait. Alkaline phosphatase con- centration was 649 U/L, while all other haematological and biochemical parameters were normal. Serum electrolytes were within normal limits and results of an ACTH stimulation testb again showed a mildly sub-normal post-stimulation cortisol con- centration (Table 2).
Six months after surgery (Day 213) the dog re-presented with possible recent increases in appetite and thirst. Serum electrolyte concentrations were normal. An ACTH stimulation testb was performed, with a high basal but normal post-stimulation corti- sol (Table 2). A low-dose dexamethasone suppression testb was performed 4 days later and normal cortisol concentrations (less than 5 nmol/L at 4 and 8 hours) were observed. Based on these findings, relapse of HAC was considered unlikely.
Nineteen months after surgery (Day 640) the dog re-presented with recent increases in water intake and appetite, thinning of the hair coat, urinary incontinence, coughing and weight loss. Blood biochemistry analyses performed by the referring veterinarian showed increases in alkaline phosphatase, alanine aminotransferase, lipase, cholesterol and creatine kinase. Physical examination showed loss of 2.0 kilograms body weight since the previous visit, a sparse truncal hair coat and a grade V/VI pansystolic left apical cardiac murmur. Plasma potassium concentration was normal and there was a mild metabolic and respiratory alkalosis (Table 2). Abdominal ultrasound examination showed a large, hyperechoic liver and an ovoid, irregularly-marginated nodule measuring 11.3 x 9.2 ×7.2 mm adjacent to the caudal vena cava
in the right cranial dorsal abdomen. The nodule consisted of a central echogenic region surrounded by hypoechoic tissue and was presumed to be local regrowth of the right adrenal gland. Thoracic radiographs showed cardiomegaly with left atrial enlargement, pulmonary vein distension and a perihilar interstitial lung pattern with multiple small interstitial pulmonary nodules. Pleural fissure lines suggested a small volume of pleural effusion. The radiographic diagnosis was probable metastatic pulmonary neoplasia and congestive heart failure. Medical management of congestive heart failure was commenced with benazepril and frusemide, with the aim of monitoring plasma potassium and adding a ‘potassium-sparing’ diuretic if hypokalaemia recurred. Due to refractory coughing, euthanasia was performed by the referring veterinarian on Day 655; necropsy examination was not permitted.
Discussion
The diagnosis of ADH in this patient was based on supportive historical and clinical signs, laboratory abnormalities, confirmatory screening tests for HAC and the presence of an adrenal mass histologically confirmed as an adrenocortical carcinoma. Further endocrine testing to investigate hypokalaemia showed increased DOC and decreased aldosterone concentrations. Following resection of the mass, a long period of clinical normality ensued without specific therapy until the detection of metastatic disease 19 months later.
In dogs, hypokalaemia may occur secondary to decreased potassium intake, translocation of potassium across cell membranes and excess gastro-intestinal or urinary potassium loss;7 in this case, marked hypokalaemia with an increased urinary fractional excretion of potassium confirmed excessive kaliuresis. This may be due to mineralocorticoid excess, administration of diuretics, or renal tubular acidosis;7 the history and concurrent clinical and laboratory findings in this patient allowed a diagnosis of mineralocorticoid excess to be made.
Although hypokalaemia is considered to be of little clinical significance in dogs with HAC,1 Ling and others8 reported that 25 of 52 dogs with HAC had hypokalaemia, with potassium concentration as low as 2.8 mmol/L. Meijer? reported that hypokalaemia occurred in 45% of dogs with ADH, compared to 5% with PDH. Metabolic alkalosis (33%)10 and hypertension (86%)11 also occur commonly in canine HAC. Muscle weakness may be observed when blood potassium falls below 3.0 mmol/L due to hyperpolarisation of excitable cell membranes and is particularly noted with acute changes in extracellular potassium concentration. Ischaemic muscle injury may also occur due to decreased potassium- mediated vasodilation during exercise7 and may have contributed to the increase in creatine kinase observed in this case. Neuromuscular complications are common in HAC, with approximately 75 to 85% of dogs developing muscle atrophy and weakness due to ‘steroid myopathy’.1,12 Less common neuromuscular complica- tions of HAC include myotonia and neuropathy.1,12 In this case the episodes of paresis were acute in onset, worsened with exertion and were clearly associated with severe hypokalaemia, although it
is possible that other neuromuscular complications were also present and contributed to weakness.
Mineralocorticoid excess states cause hypokalaemia, metabolic alkalosis and moderate to severe hypertension and may be seen in human patients with primary mineralocorticoid excess disorders and primary glucocorticoid excess.13,14 The latter most commonly occurs in patients with ectopic ACTH production syndromes, in which hypercortisolaemia can be extreme and may result in emergency presentations.15 Extremely high concentrations of cortisol exert mineralocorticoid effects through inactivation of the ‘gatekeeper enzyme’ 11-beta-hydroxysteroid dehydrogenase-2 (11-B-HSD-2). This enzyme, found in close association with type 1 corticosteroid receptors (mineralocorticoid receptors), inactivates cortisol and allows aldosterone to bind the type 1 receptor.16 Cortisol and aldosterone have similar affinities for type 1 receptors and, given the markedly greater circulating concentrations of cortisol, it is the activity of 11-B-HSD-2 that allows aldosterone to exert its effects on the distal nephron and other target tissues in the normal individual.16 11-ß-HSD-2 may become saturated in hypercortisolaemic states, permitting cortisol to bind the type 1 receptor and exert an aldosterone-like effect.2 Mean plasma cortisol concentration in dogs with PDH and ADH are not significantly different17 and the significance of 11-B-HSD-2-overload inactivation in canine HAC is unknown. Two cases of suspected ectopic ACTH production syndrome have been reported in dogs, both exhibiting profound hypoka- laemia (as low as 2.2 mmol/L) and hypercortisolaemia;18,19 in one case, hyporeninaemia and hypoaldosteronaemia were confirmed.18 In our patient, we did not demonstrate extreme hypercortisolaemia, although as the timing of cortisol assays did not coincide with severe hypokalaemia we cannot discount that 11-ß-HSD-2-overload inactivation was a possible mechanism of apparent mineralocorticoid excess.
The production of intermediary adrenal steroids with direct mineralocorticoid effects is also considered to contribute to signs of mineralocorticoid excess in human hypercortisolism.13 Increased concentrations of intermediary steroids such as DOC, with concurrently low aldosterone, are a marker of adrenocortical malignancy in humans due to inefficiency of the steroid biosynthesis pathways within the tumour.2,20 In our patient, DOC was moderately increased compared to control dogs and may have contributed to the signs of mineralocorticoid excess. Unlike aldosterone, DOC is primarily produced in the zona fasciculata of the adrenal gland2 and it is possible that this cortisol-producing tumour was also secreting DOC. DOC-producing adrenal carcinoma21 and corticosterone and aldosterone-producing adrenal carcinoma22 associated with hypokalaemia and paresis, but not hypercortisolaemia, have been described in dogs. Other unmeasured intermediary steroids or their metabolites (such as corticosterone or 19-Nor-DOC, a potent mineralocorticoid) have also been implicated in mineralocorticoid excess states2,20 and may have been contributory in this case.
Aldosterone synthesis is exquisitely sensitive to change in plasma potassium concentration2 and the low aldosterone concentrations
Cholesterol
CYP11A1
Pregnenolone
3-b-HSD II
CYP17
Progesterone
17-a- hydroxypregnenolone
CYP21A2
CYP17
11-deoxycorticosterone
3-ß-HSD II
17-
19-Nor-DOC
CYP11B1
hydroxyprogesterone
Corticosterone
CYP21A2
CYP11B1
CYP11B2
11-deoxycortisol
21-deoxycortisol
18-hydroxy corticosterone
CYP11B1
CYP21A2
CYP11B2
Cortisol
Aldosterone
observed in our patient represent a physiologically appropriate response to hypokalaemia. Low aldosterone concentrations also occur with adrenocortical malignancy due to inhibition of the mitochondrial cytochrome P450 enzyme CYP11B2 (aldosterone synthase; Figure 4) by accumulated precursor steroids and cortisol.2,20 As plasma renin activity was not measured in our patient, we cannot exclude that hyperreninism contributed to hypokalaemia and hypertension; however in humans with hypertension and adrenal carcinoma, plasma renin activity is usually suppressed.13
Unregulated mineralocorticoid activity promotes excess sodium retention, potassium excretion and hydrogen ion excretion due to increased activity and number of transmembrane ion pumps in the distal nephron.7 Tubular fluid electronegativity from avid sodium retention and high distal tubular flow rates from polyuria further promote urinary potassium and hydrogen ion loss, augmenting hypokalaemia and metabolic alkalosis.7 Sodium and water retention leads to hypertension, although mineralocorticoid-independent mechanisms also contribute to the pathogenesis of hypertension in HAC.11 This trinity of hypokalemia with kaliuresis, alkalosis and hypertension characteristic of mineralocorticoid excess syndromes was clearly observed in this dog prior to removal of its adrenal mass. Metabolic alkalosis was adjudged to be the primary acid-base disturbance in this case due to the calculated base excess present,23 with respiratory alkalosis complicating the initial presentation. This
was thought to be due to hyperventilation associated with hyperadrenocorticism and stress; the finding of a normal arterial partial pressure of oxygen ruled out a ventilation:perfusion mismatch, such as is seen in pulmonary thromboembolism. Subsequent blood gas analysis showed persistence of metabolic alkalosis with adequate respiratory compensation, supporting this interpretation.
It is noteworthy that normokalaemia was observed on Day 34, two days after KTZ was discontinued; however as electrolytes and cortisol were not measured during administration of KTZ (Days 20 to 31), its efficacy in controlling HAC and possible role in restoring normokalaemia in this case is unclear. As the inhibi- tory effects of KTZ on cortisol synthesis last less than 24 hours,17 control of HAC was inadequate when assessed by ACTH stimulation testing on Day 34. It is possible that administration of KTZ decreased kaliuresis during Days 20 to 31 and that restoration of intracellular potassium stores allowed temporary maintenance of plasma potassium after its cessation. It is also possible that translocation of intracellular potassium associated with acidosis during the brief episode of illness at this time temporarily increased plasma potassium concentration, however blood gas measurements were not taken at this time. DOC, a possible contributor to hypokalaemia in this case, is increased by KTZ’s inhibition of CYP11B124 (11ß-hydroxylase; Figure 4) but 19-Nor-DOC, a product of CYP11B1, decreases.25 This may suggest a greater role for this metabolite of DOC in the patho- genesis of mineralocorticoid excess, as has been noted previously.2 KTZ was discontinued due to clinical signs and laboratory abnormalities compatible with KTZ-induced hepatotoxicity.26 Reported histological findings associated with KTZ-induced hepatotoxicity in dogs include enlarged portal triads, bile duct proliferation and mononuclear cell infiltration,27 whilst centri- lobular necrosis is the predominant lesion in humans.28 The sig- nificance of the mild periportal hepatitis noted in hepatic biopsies at this time is uncertain and may partially explain the increased hepatocellular enzymes noted on initial presentation.
Surgical resection of the adrenal mass resulted in resolution of HAC and hypokalaemia, consistent with a causal relationship between excessive adrenal steroid concentrations and hypokalaemia. A unilateral retroperitoneal adrenalectomy may reduce postoper- ative morbidity such as the pancreatitis observed in this patient, but a ventral midline approach may facilitate inspection of both adrenal glands and detection of intra-abdominal metastases.29,30 Intracapsular dissection of the tumour was required in this case due to the extensive network of blood vessels present. Resection and patching of the adjacent caudal vena cava, which may have permitted a more definitive excision, was not attempted due to concerns that poor tissue healing and hypercoagulability associ- ated with HAC may have resulted in thrombosis or rupture at the venotomy site. Despite this limitation, the 19-month post- surgical survival time seen in this patient is similar to the 778- day median survival time recently reported for adrenal carci- noma.31 We did not perform further adrenal function testing when tumour recurrence was detected, as serious concurrent
SMALL ANIMALS
disease (congestive heart failure) was present. It is unknown whether this recurrent tumour tissue was hormonally functional and although there were clinical signs consistent with HAC present, there was no relapse of hypokalaemia.
Clinically significant hypokalaemia is not generally considered to occur in canine HAC, but severe acute hypokalaemia with pare- sis was observed in this case of ADH. Hypokalaemia has been reported to be more common in ADH than in PDH,9 although other studies have not confirmed this association.32 Investigation of the aldosterone biosynthesis pathway has been shown to be useful in the prediction of biological behaviour of human adrenal tumours.20 In dogs, no pre-surgical parameters have been identified that allow prediction of the biological behaviour of functional adrenal tumours.32,33 Further research may ascertain whether assay of intermediary adrenal steroids in dogs may serve as a marker of biological behaviour when an adrenal mass is identified.
Acknowledgments
Dr Kylie McLaren was the referring veterinarian and her assistance is gratefully acknowledged. We also thank the many MUVH clinicians, nurses and pathology staff who assisted in the management of this case. Dr Xuguang Han of the South Eastern Area Laboratory Services endocrinology laboratory generously donated his time and expertise to perform the DOC assays.
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(Accepted for publication 22 September 2007)