Intravenous administration of levothyroxine for treatment of suspected myxedema coma complicated by severe hypothermia in a dog

A 7-year-old 50-kg (110-lb) sexually intact male English Coonhound was referred to the University of Wisconsin-Madison Veterinary Medical Teaching Hospital for evaluation of suspected tachyarrhythmia.The owner had noticed weakness, a stiff gait, and ataxia of 1.5 years' duration and, more recently, anorexia.The referring veterinarian had detected, by auscultation, a brief period of tachycardia associated with blanching of mucous membranes during physical examination of the dog.On the morning of the referral appointment, the owner discovered the dog recumbent, nonresponsive, and in an extended body position in an outdoor, insulated kennel.The ambient temperature had reached a low of -22 C (-7 F) the previous night.Another dog in a nearby kennel appeared clinically normal.At referral, the dog was comatose and cold to the touch.Bilateral rotary nystagmus was evident, and the pupils were unresponsive to light.Heart rate was 20 to 30 beats/min, the cardiac rhythm was irregular, and a peripheral pulse could not be detected.Respiratory rate was 8 breaths/min, and respirations were labored.Rectal temperature did not register on a standard thermometer; however, core body temperature was measured at 23.9 C (75 F) by a rectal thermocouple probe.The dog had a diffuse increase in skin thickness in the ventral cervical area and limbs.The coat was dry and brittle, and bilaterally symmetric alopecia of the base of the ears and caudal aspects of the thighs was evident.Ulcerative skin lesions were located over the dorsal surface of multiple coccygeal vertebrae, and straw and other debris were embedded in the wounds.Continuous electrocardiographic monitoring revealed an irregular supraventricular rhythm without visible P waves.Packed cell volume was 33%, serum total protein concentration was 8.4 g/dl, serum glucose concentration was 384 mg/dl, and BUN concentration was estimated to be between 5 and 15 mg/dl.Serum biochemical analyses and CBC obtained by the referring veterinarian 10 days earlier revealed hypercholesterolemia, normoglycemia (Table 1), and anemia (PCV, 33%; reference range, 37 to 55%).A catheter was placed in a cephalic vein, and warmed lactated Ringer' s solution (20 ml/kg [9.1 ml/lb] of body weight) was administered.Atropine (0.01 mg/kg [0.0045 mg/lb]) was administered IV in an attempt to increase heart rate, and dexamethasone (1.0 mg/kg [0.45 mg/lb] IV) was added for the management of possible cerebral edema.Oxygen was delivered by face mask, recirculating water heating pads were placed over and under the dog, and a forced-air warming unit was placed around the dog' s body.Increase in heart rate was not detected after atropine administration.Urine production was detected within 1 hour of initiating fluid therapy.Blood was drawn for serum biochemical analyses (Table 1), CBC, and coagulation tests after 1,000 ml of lactated Ringer' s solution had been administered.Serum for thyroid hormone analysis was sent to a reference laboratory.a The CBC revealed nonregenerative anemia (PCV, 31%; reference range, 37 to 55%), mature neutrophilia (13,950 cells/µl; reference range, 3,000 to 11,500 cells/µl), and lymphopenia (600 cells/µl; reference range, 1,000 to 4,800 cells/µl).Platelet count was > 137,000/µl (reference range, 145,000 to 440,000/µl), and platelets were clumped.Coagulation tests revealed activated partial thromboplastin time (APTT) of 22.5 seconds (reference range, 8.0 to 14.0 seconds), one-stage prothrombin time (OSPT) of 10.9 seconds (reference range, 5.9 to 8.5 seconds), and fibrinogen and fibrin degradation products (FDP) concentrations within the reference ranges.After a 3-hour period, body temperature reached 28.3 C (83 F), and 0.9% NaCl solution was substituted for the lactated Ringer' s solution.Sinus P waves became apparent with each QRS complex on the electrocardiogram, and heart rate was 48 beats/min.After 4 hours of warming, the dog was responsive, and cranial nerve abnormalities resolved.Shivering was not observed throughout the warming process.Core body temperature reached 35.4 C (95.7 F) by 7 hours, heart rate was 68 beats/min with a sinus arrhythmia, and the dog ate food when offered.A tentative diagnosis of profound hypothyroidism was made on the basis of dermatologic abnormalities, hypercholesterolemia, nonregenerative anemia, and