subacute thyroiditis Flashcards
definition of subacute thyroiditis
self limited inflammation of the thyroid gland
triphasic clinical cause lasts from a few wks to many mo
characterised by transient thyrotoxicosis, hypothyroidism then return to euthyroid
epidemiology of subacute thyroiditis
female more
seasonal variation - highest incidence in summer - typical for viral infections
aetiology of subacute thyroiditis
viral
occur after URTI
Post-convalescent viral titres of many common viruses (influenza, adenovirus, mumps, coxsackie, echo, H1N1) are elevated and then decrease in patients after the diagnosis of subacute granulomatous thyroiditis.
Histocompatibility studies show a predominance of HLA-Bw35 in patients with subacute granulomatous thyroiditis
Familial cases of this thyroiditis occur and are associated with HDL-B35.
pathology of subacute thyroiditis
destructive thyroiditis that results in the release of preformed thyroid hormones, in the form of thyroglobulin, into the circulation
Thyroglobulin is degraded by serum proteases into the thyroid hormones levothyroxine (T4) and triiothyronine (T3). – The thyroid is often enlarged and firm to palpation
RF for subacute thyroiditis
viral infection
HLA-Bw35 and B35
signs and symptoms of subacute thyroiditis
neck pain
tender, firm, enlarged thyroid
fever
palpitations
myalgia
malaise
tremor
heat intolerance
Ix for subacute thyroiditis
TSH - suppressed initially, in recovery/hypothyroid phases level will be variable
total T4, T3, T3 resin uptake and free thyroxin index - all elevated - follow up every 4wks until levels remain normal
T3:4 ratio - <15:1
radioactive iodine uptake - low during thyrotoxic phase, may be elevated in recovery from hypothyroidism
ESR - elevated
CRP - elevated
antithyroid Ab (thyroid peroxidase Ab) - normal or mildly elevated
Mx of subacute thyroiditis - hyperthyroid phase
hyperthyroid phase - NSAIDs and corticosteroids to help with symptoms (ie pain)
opioids if necessary for analgesia
if tachycardia, anxiety and or tremor are troublesome - B blocker or CCB. B blocker indicated in sinus tachy, CCB if B blockers are CI eg in pt with bronchospasm and asthma
a saturated solution of potassium iodide or iopanoic acid along with high doses of corticosteroids such as oral prednisolone can prevent T4 –> T3. T4 more bioactive than T3 - done in severe thyrotoxicosis
treatment of subacute thyroiditis - hypothyroid phase
supportive
if symptoms interfere with daily activities - moderate levothyroxine for 6mo with no taper
TSH checked every 4-6wk with levothyroxine
withdraw after 6mo to see if endogenous func has returned to normal
6wk after stopping TSH level should be rechecked - if high re give levothyroxine for permenant hypothyroidism
complications of subacute thyroiditis
thyroid storm - degree of thyroid elevation can be really high = physiological decompensation or thyroid storm
long term hypothyroidism
prognosis of subacute thyroiditis
most have complete and spontaneous recovery
thyroid gland may exhibit irregular scarring between islands of residual functioning parenchyma - may need perm levothyroxine
unlikely to recur
why are anti-thyroid hormones ineffective in subacute thyroiditis
the hyperthyroidism is from release of pre-made hormone - stopping more production makes no difference
phases of subacute granulomatous thyroiditis
- thyrotoxic phase 4-6wk
- acute viral like illness with neck pain, fever, myalgias, malaise, pharyngitis which precedes severe neck pain that may start on one side and migrate to the contralateral side
- thyroid destructive phase with high T3 4
- thyroid uptack low
- ESR high
- hypothyroid phase - 2-6mo
- thyroid hormone levels mildly or moderately low
- thyroid uptake variable
- thyroid autoAb levels are variably elevated
- euthyroid phase
- thyroid function returns to normal
- histology returns to normal
