AKT · Endocrine/Paraneoplastic & neuroendocrine

Carcinoid syndrome

Serotonin-secreting neuroendocrine tumour (often with hepatic metastases)

Overview

The clinical syndrome of a serotonin- (and vasoactive amine-) secreting neuroendocrine tumour, usually midgut, that has metastasised to the liver (so the secreted amines bypass hepatic first-pass metabolism). Episodic FLUSHING, DIARRHOEA and bronchospasm, with right-sided cardiac valve fibrosis (TIPED) over time. Diagnosed by urinary 5-HIAA; treated with somatostatin analogues.

Recognise

Episodic FLUSHING (dry, of the face/neck), secretory DIARRHOEA, abdominal cramps, wheeze/BRONCHOSPASM
Right-sided heart valve fibrosis (tricuspid regurgitation/pulmonary stenosis) — the lungs inactivate serotonin, sparing the left heart; pellagra (niacin diversion)
Carcinoid CRISIS (profound flushing, hypotension/hypertension, bronchospasm) can be precipitated by anaesthesia/tumour handling

Red flags

Carcinoid crisis (peri-procedure) → octreotide cover
Right heart failure from carcinoid heart disease

Differentials & how to tell them apart

Phaeochromocytomaparoxysmal headache/palpitations/sweating with raised metanephrines (not 5-HIAA)

Menopausal flushing / mastocytosisflushing without secretory diarrhoea / raised 5-HIAA

VIPomaprofuse WATERY diarrhoea + hypokalaemia (WDHA) rather than flushing-dominant

Investigations

24-h urinary 5-HIAA (serotonin metabolite — raised); plasma chromogranin A; imaging/octreotide (somatostatin-receptor) scan to localise; echocardiography (right-sided valves).

Management

Somatostatin analogue (octreotide) + tumour resection/debulking

1Confirm with urinary 5-HIAA/chromogranin A and localise (octreotide scan); echocardiogram for valve disease. Control symptoms with a somatostatin analogue (octreotide/lanreotide).Gate: Symptoms appear once there are LIVER metastases (amines bypass hepatic metabolism); cover any procedure/anaesthetic with octreotide to prevent carcinoid CRISIS
2Resect/debulk the tumour and hepatic metastases; peptide receptor radionuclide therapy; manage carcinoid heart disease; niacin for pellagra.

Somatostatin analogue (octreotide/lanreotide) — first-line symptom control + slows tumour; covers carcinoid crisis perioperatively

Surgery / liver-directed therapy — resection/debulking of tumour and hepatic metastases

Niacin supplementation — prevents pellagra (tryptophan diverted to serotonin)

Key points

Flushing + secretory diarrhoea + bronchospasm + right-sided valve disease = carcinoid syndrome → 5-HIAA, octreotide. It needs liver mets to be symptomatic. Cover procedures with octreotide (crisis).

Monitor & prognosis

5-HIAA/chromogranin A; echocardiogram; imaging.

Often indolent; liver/valve disease drive morbidity.

Source: ENETS/UKINETS; StatPearls