Updated: 10/27/2018

Hypothyroidism

Topic
Review Topic
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Questions
12
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Evidence
7
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Snapshot
  • A 40-year-old woman presents to her primary care physician with complaints of increased fatigue and a 10-lb weight gain over the last 2 months. She states that she "feels cold" all the time, has decreased energy, and is experiencing worsening constipation. On physical exam, her pulse is 45/minute, her skin is dry and cold, and her lateral eyebrows are thinned. She also has delayed deep tendon reflexes. 
Introduction
  • Inadequate thyroid hormone in tissues
  • Most commonly caused by Hashimoto's thyroiditis
  • Less common causes include
    • subacute or postpartum thyroiditis
    • iatrogenic causes (inadequate replacement after surgical ablation)
    • drugs
      • iodide
      • amiodarone
        • check a TSH and pulmonary function tests prior to starting 
      • sulfonamides
      • lithium
    • pituitary dysfunction
  • Myxedema refers to
    • hypothyroidism with mucopolysaccharides deposits in the dermis
  • Subclinical hypothyroidism
    • clinical entity with elevated TSH but normal T3/T4 values
    • does not require treatment unless
      • presence of anti-TPO antibodies
      • clinical symptoms of hypothyroidism
        • hyperlipidemia
        • menstrual dysfunction
Presentation
  • Symptoms 
    • weakness and fatigue
    • cold intolerance
    • constipation
    • weight gain
    • depression
    • menstrual irregularities
    • galactorrhea 
      • thyrotropin-releasing hormone can stimulate prolactin secretion
    • hoarseness
    • myopathy
  • Physical exam
    • dry, cold skin
    • edema with puffy face, eyelids, and hands
    • (myxedema) skin
    • thinning of lateral eye brows
    • bradycardia
    • delayed relaxation of the deep tendon reflexes
Evaluation
  • Labs  
    • elevated TSH is most sensitive measure  
    • decreased serum and free T4
    • may have megaloblastic anemia
    • may have hyponatremia
    • may have hyperlipidemia
    • may have mild elevation in creatnine kinase
    • may have mild elevations in ASt and ALT
  • Scan shows < 10% radionucleotide uptake
Differential Diagnosis
  • Anxiety, neurosis, mania, pheochromocytoma, chronic alcoholism, myopathy, myasthenia gravis, dental disease
Hashimoto's Disease
  • Autoimmune lymphocytic infiltration of thyroid gland
  • Usually in females age 30-50
    • 8:1 female to male ratio
  • Diagnosis confirmed by antithyroid peroxidase (TPO) antibodies
  • Early in disease, patients may have normal TSH and normal free T4
  • Treat with lifelong levothyroxine (a thyroid hormone replacement)
    • importantly the dose must be increased during pregnancy
Subacute Thyroiditis
  • Seen following flu-like illness with soar throat and fevers
  • Presents with jaw / tooth pain
  • Initially looks like hyperthyroidism as gland spills T4
  • Later converts to hypothyroidism
  • Treatment
    • aspirin
    • cortisol for severe disease
  • Usually self-limiting and resolves in weeks to months
Resistance to Thyroid Hormone (RTH)
  • Syndrome characterized by reduced end-organ responsiveness to thyroid hormone
  • Caused by mutations in the TH receptor (TR) beta gene
  • Diagnosis is based on persistent elevations of serum free T(4) and T(3) levels in the absence of TSH suppression
  • Features in children: failure to thrive, growth retardation, ADHD
  • Features in adults: goitre, thyrotoxic cardiac symptoms
Myxedema coma
  • The only emergent hypothyroid condition
  • Precipitated by
    • cold exposure
    • infection
    • analgesics
    • drugs
    • spontaneous
  • Presentation
    • stupor
    • coma
    • seizures
    • hypotension
    • hypoventilation
  • Treatment
    • IV levothyroxine
    • hydrocortisone
    • mechanical ventilation
 

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Questions (12)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M3.EC.82) A 40-year-old woman presents to her primary care physician for an annual check-up. She complains of intermittent fatigue. Laboratory tests are notable for the following:

TSH, serum: 8.2 mU/L (normal 0.5-5.0 mU/L)
Thyroxine (T4), serum: 9.8 ug/dL (normal 5-12 ug/dL)

Which of the following other conditions, if present, would merit treatment with thyroxine? Review Topic

QID: 103572
1

Tender thyroid gland

0%

(0/4)

2

High erythrocyte sedimentation rate (ESR)

0%

(0/4)

3

Hypercholesterolemia

100%

(4/4)

4

Proptosis

0%

(0/4)

5

Hand tremor

0%

(0/4)

M2

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PREFERRED RESPONSE 3

(M2.EC.66) A 37-year-old female presents to a general medical clinic with muscle weakness. Review of systems also reveals fatigue and chronic constipation. Vital signs reveal HR 64, BP 110/80, RR 12 and T 36.4. Physical examination is notable for muscle weakness at the hips and shoulders. Initial laboratory testing reveals a normal erythrocyte sedimentation rate but an elevated creatine kinase. What is the next step in management? Review Topic

QID: 104391
1

Refer to a rheumatologist

4%

(3/78)

2

Send thyroid stimulating hormone and T4

78%

(61/78)

3

Send rheumatoid factor

1%

(1/78)

4

Send ANA

14%

(11/78)

5

Send AM Cortisol

0%

(0/78)

M2

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PREFERRED RESPONSE 2
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(M2.EC.87) A 31-year-old female with a past medical history of follicular thyroid cancer treated two years prior with a total thyroidectomy followed by radioactive iodine ablation presents to her gynecologist with questions relating to pregnancy. She and her partner are thinking about getting pregnant, but she is concerned about her thyroid replacement hormone, specifically the complications of being hypothyroid during pregnancy. She wants to know how her levothyroxine dosing should be handled prior to conception and during her pregnancy. Which of the following would be an appropriate response to this patient's concerns? Review Topic

QID: 104412
1

Your current dose will need to be increased before conception to reduce the potential fetal complications.

0%

(0/3)

2

Your current dose will only need to be increased during pregnancy, not before.

100%

(3/3)

3

Your current dose will only need to be increased before pregnancy, not during.

0%

(0/3)

4

Your current dose will be sufficient for her and the fetus during pregnancy.

0%

(0/3)

5

Your pregnancy is at increased risk of complications because of hypothyroidism regardless of the dose.

0%

(0/3)

M2

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PREFERRED RESPONSE 2

(M3.EC.3) A 53-year-old female presented to her primary care physician for an annual check-up. She does not smoke, use drugs, or consume alcohol. The patient currently takes no medications. Routine blood tests demonstrate a TSH level of 9.5 uU/mL (normal 0.35 to 5.0 uU/ml). Her T3/T4 levels are within normal limits. The initiation of treatment for hypothyroidism would be indicated for all EXCEPT which of the following findings? Review Topic

QID: 103493
1

Pretibial myxedema

56%

(5/9)

2

Presence of antithyroid peroxidase (anti-TPO) antibodies

22%

(2/9)

3

Hyperlipidemia

0%

(0/9)

4

Constipation

11%

(1/9)

5

Decreased sweating

11%

(1/9)

M2

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PREFERRED RESPONSE 1
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