--- module: 023-02 language: en chapter: 23 title: "Hypothalamic-Pituitary Control and Endocrine Feedback" module_title: "Endocrine pattern recognition, assay interference, and pituitary emergencies" source_sha256: e9a519a3249013cc2cfefbd93d4aed9f9bd6f8eac9b79a57b641533cf18b03d4 --- # Endocrine patterns, assay interference, pituitary emergencies ## Concentration as an integrated signal ### Secretion, binding, conversion, clearance ### Effect depends on receptors and sensitivity #### Normal level can coexist with resistance ### Binding protein raises total concentration #### Pregnancy and oestrogen raise totals #### Protein loss and liver disease lower totals ### Local conversion #### Deiodinases activate or inactivate thyroid hormone #### 11-beta dehydrogenase gates mineralocorticoid receptors #### Aromatase converts androgens to oestrogens ## Paired tests localise the axis ### Low target, high trophic: primary failure ### Low target, low or normal trophic: central #### Normal-range trophic can be pathological ### High target, suppressed trophic: primary excess ### High target, non-suppressed trophic #### Interference, resistance, or central autonomy #### Confirm before imaging ### Severe acute illness distorts feedback #### Repeat after recovery unless urgent ## Pulses, cycles, and sample timing ### Growth hormone undetectable between pulses #### Random value cannot diagnose deficiency ### Cortisol follows a circadian rhythm #### Shift work, illness, steroids alter results ### Gonadotropins vary with cycle and life stage ### Prolactin rises with sleep, stress, medicines ### Repeat mild abnormalities under control ## Assay interference ### Heterophile antibodies, autoantibodies, biotin ### Suspect when results conflict with physiology ### Biotin: false highs or false lows by assay #### Mimics thyrotoxicosis, hides trophic rise ### Hook effect saturates assay antibodies #### Large mass with mild prolactin: dilute ### Macroprolactin: elevation without phenotype ### Confirm: other platform, dilution, mass spectrometry ## Dynamic tests ask a directional question ### Stimulation assesses reserve #### Synthetic adrenocorticotropic hormone tests cortex #### Early central deficiency may still respond #### Insulin hypoglycaemia carries real risk ### Suppression assesses autonomy #### Dexamethasone: autonomous cortisol escapes #### Glucose fails to suppress in acromegaly ### Water deprivation separates intake from deficit #### Copeptin as a stable surrogate ## Pituitary mass effects ### Beneath chiasm, beside cavernous sinus ### Crossing nasal fibres: temporal field loss ### Lateral extension: eye movement, facial sensation ### Stalk compression raises prolactin modestly ### Diabetes insipidus suggests another lesion ### Formal visual fields beat confrontation ## Apoplexy and hormone-order safety ### Haemorrhage or infarction, often in a tumour #### Mimics subarachnoid haemorrhage or meningitis ### Acute adrenocorticotropic loss is immediately dangerous #### Empirical glucocorticoid without delay ### Thyroid raises demand and cortisol clearance #### Thyroid before cortisol precipitates crisis ## Growth, prolactin, and gonadal consequences ### Growth excess remodels tissues and heart #### Normal growth factor does not reverse structure ### Prolactin suppresses pulsatile releasing hormone #### Infertility, sexual dysfunction, bone loss #### Coordinate psychiatric medicine changes ### Separate central from functional suppression ### Sex steroids do not restore gamete production ## Water balance and masked diabetes insipidus ### Cortisol deficiency raises vasopressin #### Cortisol treatment unmasks diabetes insipidus ### Desmopressin excess causes hyponatraemia ### Nephrogenic: remove cause, reduce solute ### Review intake, urine, sodium, thirst together ## Incidentalomas and long-term care ### Manage from function outward ### Stable diameter does not mean stable function ### Final report: axis, level, timing, interference ### Replacement needs change over time #### Adrenal: stress dosing, emergency injection #### Patient knows deficiency and excess signs