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Unusual feline endocrine diseases (Proceedings)

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Apr 01, 2010

I. Thyroid Storm – see previous notes

II. Hyperadrenocorticism
     A. a rare disorder in cats
     B. Etiology
          1. Pituitary adenoma (85%)
          2. adrenal adenoma
          3. adrenal carcinoma
     C. Clinical presentation
          1. Middle-older aged cats (5-16 years), no breed or sex predilection
          2. Most cats have concurrent insulin-resistant diabetes mellitus
          3. Thin, fragile skin
          4. Large non-healing cutaneous wounds
          5. Polyuria/polydipsia
          6. Polyphagia
          7. Recurrent cutaneous, upper respiratory, and urinary tract infections
          8. Lethargy
          9. Muscle atrophy
          10. Weakness
          11. abdominal enlargement
          12. alopecia/failure to regrow hair
     D. Clinicopathologic Findings
          1. Elevated ALP and ALT
          2. hypercholesterolemia
          3. hyperglycemia
          4. mature neutrophilia, lymphopenia, eosinopenia (stress leukogram)
          5. glucosuria
          6. lack of urine concentrating ability
          7. proteinuria
          8. bacteriuria, pyuria
     E. Diagnosis
          1. Screening tests
               a. Low-dose dexamethasone suppression test
                    (1) use 10 x dexamethasone dose as for dogs
                    (2) 0.1 mg/kg dexamethasone IV
                    (3) serum cortisol measured 0, 4, 8 hr
                    (4) cortisol not suppressed at 4 and/or 8 hr – supports diagnosis of hyperadrenocorticism
                    (5) cannot be used as a differentiating test as in dogs
               b. ACTH-stimulation test
                    (1) 40-50% of cats with hyperadrenocorticism will show a normal response to ACTH
                    (2) synthetic ACTH (cortrosyn)
                         -125 mcg IM, serum cortisol samples 0, 30, 60 min.
                         -125 mcg IV, serum cortisol samples 0, 60, 90 min.
                    (3) ACTH gel – 2.2 U/kg IM, serum cortisol samples 0, 60, and 120 min
                    (4) an exaggerated response to ACTH of > 19 mcg/dl is consistent with a diagnosis of hyperadrenocorticism
          2. Differentiating tests
               a. plasma endogenous ACTH concentration
                    (1) single plasma sample submitted
                    (2) special handling of plasma depending on laboratory used
                    (3) pituitary-dependent disease: ACTH concentrations normal to high
                    (4) adrenal-dependent disease: ACTH concentrations low or nondetectable
               b. abdominal ultrasonography
                    (1) unilaterally enlarged or calcified adrenal gland supports adrenal-dependent hyperadrenocorticism
                    (2) bilaterally enlarged adrenal glands support pituitary-dependent hyperadrenocorticism
               c. magnetic resonance imaging – pituitary tumor
     F. Treatment
          1. Medical
               a. mitotane (Lysodren)
                    (1) not effective in cats
                    (2) deleterious side effects
               b. trilostane
                    (1) begin with 5 mg/kg PO q 24 and increase or decrease as necessary
                    (2) monitor with ACTH-stimulation test with the goal of having pre- and post- ACTH cortisol concentrations between 1-4 mcg/dl
                    (3) monitor serum Na/K levels
                    (4) in cats with diabetes mellitus, reduce insulin by at least 25% before starting trilostane as insulin requirements will decrease
          2. Surgical
               a. unilateral adrenalectomy
               b. bilateral adrenalectomy in cats that cannot be medicated orally
               c. control clinical signs of hyperadrenocorticism with trilostane for at least 2 weeks before surgery to heal skin lesions and control diabetes mellitus if present. Insulin dose should be decreased by at least 25% before initiating trilostane
               d. If bilateral adrenalectomy, glucocorticoid and mineralocorticoid therapy will be necessary for life.
                    (1) desoxycorticosterone pivalate (DOCP; Percorten-V, Novartis Animal Health) – 2.2 U/kg IM q 30 days
                    (2) prednisolone 0.4 mg/kg PO sid
                    (3) methylprednisolone acetate, Depomedrol, 10 mg IM q 30 days
               e. With unilateral adrenalectomy, glucocorticoid and mineralocorticoid therapy may be necessary for several weeks while the healthy adrenal gland regenerates.