Carcinoid syndrome is a paraneoplastic syndrome mediated by humoral factors released by some carcinoid tumors. The majority of neuroendocrine tumors arise from the small intestine, particularly in the ileum, and they release into the systemic circulation a variety of vasoactive substances: serotonin, 5-hydroxytryptamine, 5-hydroxytryptophan, histamine, tachykinins, bradykinin, and prostaglandins, which explain the clinical manifestations of carcinoid syndrome .
Carcinoid syndrome is rare and once it is developed, more than 50% of the patients develop CaHD that can inaugurate this syndrome in 20% of cases. It is associated with a poor prognosis .
Symptoms of carcinoid syndrome (facial flushing, hypermotility of the gastrointestinal system, bronchoconstriction, and hypotension) usually occur in patients with hepatic metastatic lesions, due to the lack of hepatic inactivation of these released hormones .
These vasoactive substances act directly on the valvular endocardium and activate a fibrotic process. Histopathology reveals fibrous plaque-like and endocardial thickening leading to thickening and retraction of the valves. In this disease, the involvement of the right-sided heart valves is predominant and may be in the form of regurgitation and/or stenosis [6, 7]. Right-sided heart failure remains a major factor of morbidity in patients with CaHD . Left-sided cardiac involvement is rarely observed (<10% of patients), particularly in the case of right-to-left shunt (a PFO) or bronchial carcinoids due to the bypassing of inactivation of serotonin within the lung .
The diagnosis is essentially based on biological examinations and echocardiography which remains the principal imaging modality in assessment of CaHD [6–10]. Biological examinations are helpful in the diagnosis of CaHD. High levels of N-terminal pro-brain natriuretic peptide (NT-proBNP), chromogranin-A (a neuroendocrine secretory protein), and urinary 5-HIAA (a metabolite of serotonin) are correlated with the progression of CaHD [11, 12]. Echocardiography shows typical valvular involvement: the tricuspid valve is constantly thickened, rigid, and retracted with restricted mobility and poor coaptation which lead to tricuspid regurgitation. Stenosing character is rarer (25% of cases) but may be associated. The pulmonary valve, which is more difficult to study, is reached in 30% of cases with regurgitation or pulmonary stenosis [10–13].
The right cavities and the inferior vena cava are dilated with or without right ventricular dysfunction . Myocardial strain allows detection of an early right ventricular dysfunction in patients with CaHD independently of valvular involvement .
Of all patients with CaHD, ≤ 10% have lesions of the left-side valve. CaHD in the left side of the heart is less severe than in the right side of the heart. Left-sided heart involvement in carcinoid syndrome happens in patients with persistent foramen ovale or bronchial carcinoid .
Patients with CaHD have a decreased life expectancy compared with patients without cardiac lesions . The treatment of patients with carcinoid syndrome is complex and involves multidisciplinary management. It is based on medical therapy, surgery of the tumor, and cardiac surgery .
Medical management consists of controlling the heart failure (diuretics agents and aldosterone antagonist) and symptoms of carcinoid syndrome. Therapy by somatostatin analogues allows improvement of symptoms and quality of life and decreases the incidence of CaHD from 50 to 20% .
New agents (telotristat and pasireotide) have shown promising results in patients with carcinoid syndrome refractory to somatostatin analogues . Telotristat etiprate is a potent inhibitor of the synthesis of serotonin. The phase III TELESTAR clinical trial has shown that Telotristat may control the bowel movements in patients with carcinoid syndrome. It represents a new option for the treatment of patients with refractory carcinoid syndrome. However, other research is required to verify the safety and the benefit to control symptoms of that new drug .
Interferon alpha can be used as a complementary treatment for somatostatin analogues in refractory carcinoid syndrome. Because of its side effects, it should be initiated by 3 MU thrice weekly and then an individual titration .
Surgical resection of the primary tumor and resection of liver metastases appear to decrease the cardiac progression in CaHD and improve prognosis . Since hepatic surgery exposes a patient to the risk of perioperative bleeding, hepatic intra-arterial treatment (transarterial chemoembolization, selective internal radiotherapy) is well suited to patients with hepatic metastases .
Valve replacement surgery or valvuloplasty is the only effective treatment for symptomatic CaHD; it improves the symptoms and increases the life expectancy of these patients . The optimal moment for valve replacement surgery is not established. However, valvular surgery is proposed when patients become symptomatic or develop ventricular dysfunction provided they have a life expectancy of at least 1 year . Bioprosthetic valves are generally preferred over a mechanical prosthesis, which requires anticoagulation for life and then exposes patients with liver metastases to the risk of bleeding in addition to the risk of prosthesis thrombosis in tricuspid position . Percutaneous valve implantation is a novel option in high-risk patients with severe CaHD, who have poor performance status and comorbidities that do not allow open surgery .
The prognosis of patients with CaHD has improved in recent years through cardiac surgery. In the Mayo Clinic, a retrospective analysis of 200 patients with CaHD found that cardiac surgery improves the prognosis and reduced the mortality related to that disease [25, 26].
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