What is carcinoid syndrome?
Carcinoid syndrome is characterised by episodic cutaneous flushing, diarrhoea, and wheezing.
Carcinoid syndrome is the result of a combination of peptides and amines secreted by advanced neuroendocrine tumours (NETs) into the bloodstream.
Who gets carcinoid syndrome?
Carcinoid syndrome affects up to 19% of people with neuroendocrine tumours, which can be present in the gut, pancreas, lung, kidney, ovaries, and testes. They are rare in children. The incidence is 1–2 per 100,000 people annually. They can occur in people with multiple endocrine neoplasia type 1 and Peutz-Jeghers syndromes.
Carcinoid symptoms are more common in those with bowel tumours, particularly when they have spread to the liver.
What causes carcinoid syndrome?
Neuroendocrine tumours can secrete bioactive amines into the bloodstream, causing symptoms of carcinoid syndrome. The most common amines and peptides are:
- Serotonin (key molecule associated with carcinoid syndrome)
What are the clinical features of carcinoid syndrome?
The main cutaneous feature of carcinoid syndrome is flushing, which occurs in 75% of cases. This is caused by transient dilation of blood vessels.
- Flushing (red brown or bright red colour) affects the face, head, neck, chest, and epigastric areas.
- It may last for several minutes to several hours (particularly in the later stages of the disease).
- The skin may be diffusely affected or mottled, with or without accompanying oedema.
- Recurrent flushing may lead to long-lasting skin changes, including telangiectasia and plethora (persistent redness).
Patients with neuroendocrine tumours may have deficiency in niacin. This manifests as a triad of dermatitis, dementia, and diarrhoea (pellagra). Clinically, patients present with erythematous skin with superficial scaling in areas exposed to sunlight.
Flushing could be spontaneous or triggered by:
- Psychological stress
- Physical stress
- Food items which are either spicy or rich in amines (eg, chocolate, kiwi, banana, avocados)
- Medications (eg, catecholamines, calcium, and pentagastrin).
Carcinoid syndrome may also cause other symptoms such as weight loss, low blood pressure, and abdominal pain.
What are the complications of carcinoid syndrome?
Carcinoid syndrome can cause carcinoid crisis, which involves cutaneous flushing, hypotension, tachycardia/arrhythmias, bronchospasm, and/or sometimes hyperthermia.
Patients with carcinoid syndrome may experience long-term complications such as carcinoid heart disease, causing valve fibrosis, nutritional deficiencies (deficiency of niacin leading to pellagra), and neuropsychiatric manifestations.
How is carcinoid syndrome diagnosed?
Carcinoid syndrome may be suspected clinically, and confirmed by finding an elevated 24-hour urine 5-hydroxyindoleacetic acid (5-HIAA), which is an indirect marker of serotonin production. The extent of tumours can be identified by CT and MR imaging, as well as specific radioisotope scanning (MIBG and octreotide scans).
What is the differential diagnosis for carcinoid syndrome?
- Irritable bowel syndrome
- Gastrointestinal motility disorders
- Celiac disease
- Acute pseudo-obstruction of the bowel
- Acute urticaria
What is the treatment for carcinoid syndrome?
Carcinoid syndrome is a paraneoplastic phenomenon, and therefore treating the underlying neuroendocrine tumour is key.
- Surgical resection of the primary tumour as well as nodal and liver metastases reduces the tumour burden.
- Tumour chemotherapy may help advanced metastatic disease as can radiopharmaceuticals.
- Symptomatic treatment with medications such as somatostatin receptor analogues (eg, octreotide) and/or interferon alfa may be used for symptoms associated with amine secretion.
Carcinoid crisis can be treated with intravenous octreotide, intravenous hydrocortisone, and/or intravenous chlorpheniramine.
What is the outcome for carcinoid syndrome?
If all of the carcinoid tumours can be resected, then prognosis is excellent. If carcinoids have metastasised to the liver or other organs, and there is evidence of progressive, recurring or relapsing disease, then the prognosis is more guarded.