Thyroid Disorders - Clinical Features MCQs

The first clinical sign of the onset of puberty in boys is an increase in testicular volume (> 4 ml). This is followed by growth of external genitalia, pubic and axillary hair growth, growth of external genitalia and deepening of voice The first sign of pubertal onset in girls is thelarche (breast development) followed by pubic hair growth and menarche. Reference : Harrison's Principles of Internal Medicine 21 st edition Page 3011

The ret proto-oncogene encodes for a receptor tyrosine kinase. In medullary thyroid carcinoma the mutation is associated with hyperfunction. Ret is associated with familial cases of medullary thyroid carcinoma and the MEN-2 syndrome. Formerly the condition was screened for with the pentagastrin suppression test, although a DNA probe for ret is now readily available and patients can be screened via a leukocyte sample. Reference: Harrison’s Principles of Internal Medicine 20 th edition Ch:378 Pg:2714-17

The RET proto-oncogene encodes for a receptor tyrosine kinase. Activating mutation in RET gene can lead to MEN 2A and MEN 2B syndromes Medullary thyroid cancer is present in 100% of MEN2A and MEN 2B syndrome cases Serum Calcitonin is used as a tumor marker in screening patients with suspected Medullary thyroid cancer. Reference: Harrison's Principles of Internal Medicine 21 st edition page 2953

Prolactin is under predominantly inhibitory control , by levels of dopamine. Prolactin levels are known to rise during pregnancy, lactation, severe stress, sleep and coitus. Mildly increased prolactin levels in the range of 400-600 mU/litre may be physiological, but higher levels require a diagnosis. Levels above 1000 imply the possibility of microprolactinoma, and levels above 5000 imply the presence of macroprolactinoma. Drug causes of Hyperprolactinaemia are, not surprisingly, the dopamine antagonists, which include metoclopramide, domperidone and the phenothiazines. Features of Hyperprolactinaemia in women include amenorrhoea, galactorrhoea, loss of libido, subfertility and features of androgen deficiency. Reference: Harrison's Principles of Internal Medicine 20 th edition Chapter:371, Page number:2660-61

Pendred syndrome is an autosomal recessive disorder causing congenital hypothyroidism with sensorineural hearing loss Mutation in Pendrin (SLC26A4) which is a chloride-iodide transporter Gene coding Pendrin is located in Chromosome 7 Pendrin, located in the apical surface of follicular cell, mediates the secretion of iodine into the colloid Reference: Harrison's Principles of Internal Medicine 21 st edition page 2935

Thyroid function tests and clinical manifestations are reviewed 4-6 weeks after starting treatment, and the dose is titrated based on unbound T4 levels. Most patients do not achieve euthyroidism until 6-8 weeks after treatment is initiated. TSH levels often remain suppressed for several months and therefore do not provide a sensitive index of treatment response. When TSH suppression is alleviated, TSH levels can also be used to monitor therapy. Though total T3 and T4 can also be used, free hormones would be the better option. Reference: Harrison's Principles of Internal Medicine 21 st edition Page:2931

Compared with normal subjects, hyperthyroid patients show significantly lower resting arterial CO2 tension, tidal volume and significantly higher mean inspiratory flow and pa(O2). This may of course lead to misdiagnosis of patients with hyperthyroidism as having hyperventilation syndrome. Patients with hyperthyroidism also show a greater ventilatory response to hypoxia than normal patients. These ventilatory changes are significantly correlated with T3 levels. Reference: Harrison's Principles of Internal Medicine 21 st edition Page:2939

The average daily production of T4 is around 80-85 mcg/day (1.6-1.8 mcg/kg) In a patient with no endogenous thyroid hormone production, the replacement dose is typically 1.6-1.8 mcg/kg The dose of thyroxine is adjusted based on the TSH value done after 6 to 8 weeks Reference: Harrison's Principles of Internal Medicine 21 st edition page 2927