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E28 Endocrinology
Thyroid Toronto Notes 2019 Hashimoto’s Thyroiditis
• mostcommonformofprimaryhypothyroidisminNorthAmerica
• chronicautoimmunethyroiditischaracterizedbybothcellularandhumoralfactorsinthedestruction
of thyroid tissue
• twomajorforms:goitrousandatrophic;bothformssharesamepathophysiologybutdifferintheextent
of lymphocytic infiltration, fibrosis, and thyroid follicular cell hyperplasia
• goitrousvariantusuallypresentswithasmall,rubberygoitreandeuthyroidism,thenhypothyroidism
becomes evident
■ associated with fibrosis
• atrophicvariantpatientsarehypothyroidfromthestart ■ associated with thyroid lymphoma
Etiology and Pathophysiology
• defectincloneofT-suppressorsleadstocell-mediateddestructionofthyroidfollicles
• Blymphocytesproduceantibodiesagainstthyroidcomponentsincludingthyroglobulin,thyroid
peroxidase, TSH receptor, Na+/I– symporter
Risk Factors
• F:M=7:1
• geneticsusceptibility:increasedfrequencyinpatientswithDown’ssyndrome,Turner’ssyndrome,
certain HLA alleles, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4)
• familyHxorpersonalHxofotherautoimmunediseases
• cigarettesmoking
• highiodineintake
• stressandinfection
Investigations
• high TSH, low T4 (not necessary to measure T3 as it will be low as well)
• presenceofanti-thyroidperoxidase(TPOAb)andthyroglobulinantibodies(TgAb)inserum
Treatment
• ifhypothyroid,replacewithL-thyroxine(analogofT4)
Myxedema Coma
Definition
• medicalemergency–severehypothyroidismcomplicatedbytrauma,sepsis,coldexposure,MI, inadvertent administration of hypnotics or narcotics, and other stressful events!
• rare;highlevelofmortalitywhenitoccurs(upto40%,despitetherapy)
Clinical Features
• hallmarksymptomsofdecreasedmentalstatusandhypothermia
• hyponatremia,hypotension,hypoglycemia,bradycardia,hypoventilation,andgeneralizededemaoften
present
Investigations
• decreasedT4,increasedTSH,decreasedglucose
• checkACTHandcortisolforevidenceofadrenalinsufficiency
Treatment
• aggressiveandimmediatetreatmentrequired
• ABCs:ICUadmission
• corticosteroids(forriskofconcomitantadrenalinsufficiency):hydrocortisone100mgq8h
• L-thyroxine0.2-0.5mgIVloadingdose,then0.1mgIVODuntiloraltherapytolerated;alsoconsider
T3 therapy
• supportivemeasures:mechanicalventilation,vasopressordrugs,passiverewarming,IVdextrose,fluids
if necessary (risk of overload) • monitorforarrhythmia
Sick Euthyroid Syndrome
Definition
• changesincirculatingthyroidhormonesamongstpatientswithseriousillness,trauma,orstress • notduetointrinsicthyroidorpituitarydisease
• initially low free T3 may be followed by low TSH and if severe illness low free T4
• withrecoveryofillness,TSHmayovershootandbecometransientlyhigh
Pathophysiology
• abnormalitiesincludealterationsin:
■ peripheral transport and metabolism of thyroid hormone ■ regulation of TSH secretion
■ thyroid function
• maybeprotectiveduringillnessbyreducingtissuecatabolism