Carcinoid Syndrome: Preclinical Models and Future Therapeutic Strategies.

Carcinoid syndrome represents a debilitating paraneoplastic disease, caused by the secretion of several substances, occurring in about 10-40% of patients with well-differentiated neuroendocrine tumors (NETs). The main signs and symptoms associated with carcinoid syndrome are flushing, diarrhea, hypotension, tachycardia, bronchoconstriction, venous telangiectasia, dyspnea and fibrotic complications (mesenteric and retroperitoneal fibrosis, and carcinoid heart disease). Although there are several drugs available for the treatment of carcinoid syndrome, the lack of therapeutic response, poor tolerance or resistance to drugs are often reported. Preclinical models are indispensable tools for investigating the pathogenesis, mechanisms for tumor progression and new therapeutic approaches for cancer. This paper provides a state-of-the-art overview of in vitro and in vivo models in NETs with carcinoid syndrome, highlighting the future developments and therapeutic approaches in this field.

Carcinoid syndrome-Symptoms and therapeutic approaches.

The carcinoid syndrome (CS) is a constellation of symptoms attributed to hypersecretion of amines, prostaglandins and polypeptides. The cardinal symptoms of CS are flushing, diarrhea and bronchospasm; however, CS may present with various symptoms and signs, as: Skin: cutaneous flushes, cyanosis, pellagra, Gastrointestinal: diarrhea, nausea, abdominal cramps, vomiting, Heart: tricuspid and pulmonic valve thickening causing right heart failure, edema, Respiratory: wheezing, dyspnea.

Clinical Features and Prognosis of Patients with Carcinoid Syndrome and Carcinoid Heart Disease: A Retrospective Multicentric Study of 276 Patients.

INTRODUCTION: Carcinoid syndrome is the most frequent functional syndrome of neuroendocrine neoplasia. It is characterized by flushing, diarrhea, wheezing, hypotension, and exanthema and may cause carcinoid heart disease. METHODS: We assessed clinical characteristics and prognosis of patients with carcinoid syndrome and carcinoid heart disease in 276 patients from 3 referral centers. RESULTS: Carcinoid syndrome patients had a mean age of 57 years (range 21-84) and a normal BMI of 24.9 (SD 4.5; range 13.8-39.6). Most primaries were of small bowel or unknown primaries with distant metastasis in 94.6%. Flushing was the most frequent symptom in 74.3% of patients, followed by diarrhea in 68.8%, and wheezing in 40.9%. Pain was described by 45.3%, weakness by 23.5%, and weight loss of >10% in 6 months by 30.1% of patients. Carcinoid heart disease was diagnosed in 37.3% of patients (n = 104) by echocardiography and involved predominantly in the tricuspid valve. Combinations with other valve defects were common. Somatostatin analogs were taken by 80.4% of patients and 17% needed additional loperamide/opium tincture. Surgery and peptide receptor radiotherapy were most frequent treatments. The median survival of patients with carcinoid syndrome after diagnosis was 9 years. Prognosis was significantly impaired by male sex and diagnosis of carcinoid heart disease but surprisingly significantly increased by the presence of symptoms flushing and weakness. DISCUSSION/CONCLUSION: Carcinoid syndrome is associated with extensive disease and primaries in small bowels or of unknown primary. Weight loss, weakness, and pain are frequent, and carcinoid heart disease is diagnosed in more than one-third of patients.

Carcinoid Heart Disease: Prognostic Value of 5-Hydroxyindoleacetic Acid Levels and Impact on Survival: A Systematic Literature Review.

BACKGROUND: Carcinoid heart disease (CHD) can develop in patients with carcinoid syndrome (CS), itself caused by overproduction of hormones and other products from some neuroendocrine tumours. The most common hormone is serotonin, detected as high 5-hydroxyindoleacetic acid (5-HIAA). This systematic literature review summarises current literature on the impact of CHD on survival, and the relationship between 5-HIAA levels and CHD development, progression, and mortality. METHODS: MEDLINE, Embase, Cochrane databases, and grey literature were searched using terms for CHD, 5-HIAA, disease progression, and mortality/survival. Eligible articles were non-interventional and included patients with CS and predefined CHD and 5-HIAA outcomes. RESULTS: Publications reporting on 31 studies were included. The number and disease states of patients varied between studies. Estimates of CHD prevalence and incidence among patients with a diagnosis/symptoms indicative of CS were 3-65% and 3-42%, respectively. Most studies evaluating survival found significantly higher mortality rates among patients with versus without CHD. Patients with CHD reportedly had higher 5-HIAA levels; median urinary levels in patients with versus without CHD were 266-1,381 versus 67.5-575 µmol/24 h. Higher 5-HIAA levels were also found to correlate with disease progression (median progression/worsening-associated levels: 791-2,247 µmol/24 h) and increased odds of death (7% with every 100 nmol/L increase). CONCLUSIONS: Despite the heterogeneity of studies, the data indicate that CHD reduces survival, and higher 5-HIAA levels are associated with CHD development, disease progression, and increased risk of mortality; 5-HIAA levels should be carefully managed in these patients.

Telotristat ethyl: a novel agent for the therapy of carcinoid syndrome diarrhea.

Carcinoid syndrome (CS), characterized by diarrhea and flushing, is present in 20% of patients with neuroendocrine tumors at diagnosis and becomes more frequent with progression. The diarrhea of CS is caused mainly by tumoral secretion of serotonin. It may not be fully controlled by somatostatin analogs, the currently indicated drugs for symptomatic relief. Telotristat ethyl is a novel inhibitor of tryptophan hydroxylase, the rate-limiting enzyme in serotonin biosynthesis. Administration of the drug decreases diarrhea in patients with CS. Telotristat ethyl was approved in February 2017 (USA) and September 2017 (European Commission) for the treatment of CS diarrhea in adults inadequately controlled by somatostatin analog alone. This drug is expected to greatly improve the health and quality of life of patients with CS diarrhea.

Retrospective review of serotonergic medication tolerability in patients with neuroendocrine tumors with biochemically proven carcinoid syndrome.

BACKGROUND: Patients with carcinoid tumors frequently could benefit from the pharmacologic treatment of depression and anxiety. However, many prescribers avoid serotonergic medications due to the theoretical risk of exacerbating carcinoid syndrome. METHODS: The authors conducted a retrospective chart review of patients with carcinoid tumors and elevated serotonin levels (as measured by 24-hour urine 5-hydroxyindoleacetic acid [5-HIAA]) at Dana-Farber/Brigham and Women's Cancer Center who initiated treatment with serotonergic antidepressants after a carcinoid diagnosis from 2003 to 2016. Each medication regimen was categorized based on the presence of adverse interactions as defined by clinical worsening of symptoms of carcinoid syndrome in the absence of progressive disease that temporally correlated with a serotonergic medication trial. RESULTS: A total of 73 serotonergic regimens received by 52 patients were included in the primary analysis. Among these medication trials, 8.2% of the regimens (6 regimens) were categorized as being associated with a likely adverse interaction, 61.6% of the regimens (45 regimens) were categorized as having no adverse reaction, 9.6% of the regimens (7 regimens) were categorized as an unlikely adverse reaction, and 20.6% of the regimens (15 regimens) were categorized as unknown. It is interesting to note that none of the 73 trials resulted in a carcinoid crisis requiring emergency care or hospitalization. Only 3 patients discontinued serotonergic medications due to worsening carcinoid syndrome. CONCLUSIONS: Serotonergic medications appear to be a safe option for the treatment of depressive and anxiety symptoms in the majority of patients with neuroendocrine tumors and carcinoid syndrome. In the current study, <10% of patients developed a combination of flushing, diarrhea, and bloating after the initiation of serotonergic medications. Clinicians can begin with low doses, monitor these symptoms, and reduce the dose or discontinue the medication if necessary. Cancer 2017;123:2735-42. © 2017 American Cancer Society.

The Influence of Preoperative Symptoms on the Death of Patients with Small Intestinal Neuroendocrine Tumors.

BACKGROUND: Small intestinal neuroendocrine tumors (SI-NETs) are uncommon tumors with an annual incidence of about 1 per 100,000. Usually, SI-NETs have a slow progression, and patients often present with generalized disease. Many patients do well, and the disease has a relatively favorable 5-year survival rate. Some SI-NETs, however, have a more negative prognosis. This study aimed to establish prognostic factors for death identifiable at primary surgery. METHODS: A nested case-control study investigated 1150 patients from the cohort of all patients with a diagnosis of SI-NETs in Sweden between 1961 and 2001. The study cases consisted of all patients who died of SI-NETs during the study period. Each case was assigned a control subject matched by age at diagnosis and calendar period. Possible prognostic factors [gender, degree of symptoms, indication for surgery, World Health Organization (WHO) stage] were evaluated in uni- and multivariable analyses. RESULTS: The patients with symptomatic disease had an increased risk of dying. The indication for primary surgery influenced survival, showing a more negative prognosis for elective surgery. The WHO stage influenced survival, and stage 4 patients had an almost threefold risk of dying compared with stages 1 to 3b patients. CONCLUSIONS: This study showed that preoperative symptoms are important in prognostication for SI-NETs. Hormonal symptoms generally signify a patient with a more advanced disease stage and a worse prognosis. Including symptomatic disease together with the WHO stage and grade could possibly increase the accuracy of prognostication.

Development of a gastric carcinoid tumor following allogeneic hematopoietic stem cell transplantation for early T-cell precursor acute lymphoblastic leukemia.

Gastric carcinoid tumor is rarely diagnosed in children. We report a case of gastric carcinoid tumor that occurred after allogeneic HSCT. A 13-year-old girl with ETP acute lymphoblastic leukemia underwent allogeneic HSCT from a 7/8 HLA-matched unrelated donor. She presented with rashes, abdominal pain, and diarrhea, which were suggestive of GVHD, 7 months after HSCT. Immunosuppressive agents failed to resolve these symptoms well. After a series of evaluations, carcinoid syndrome caused by a gastric carcinoid tumor was diagnosed. The tumor was located in the antral region and resulted in partial gastric outlet obstruction. She received subtotal gastrectomy with regional lymph node dissection. However, she had a flare-up of GVHD 1 month after surgery, and immunosuppressive therapy was intensified accordingly. Although her GVHD was getting better, she developed respiratory syncytial viral pneumonia with rapid progression to respiratory failure. She died of multiple organ failure 2 months postoperatively. This is the first pediatric case of a gastric carcinoid tumor following allogeneic HSCT. Our case also highlights the necessity for pediatric transplant physicians to be aware of carcinoid syndrome caused by this rare tumor in the setting of GVHD with poor response to immunosuppressive agents.

Coronary Vasospasm and Bowel Ischemia in a Patient with Metastatic Gastrointestinal Carcinoid.

We describe a case of a 60-year-old female with a history of metastatic carcinoid disease with liver involvement who developed coronary vasospasm and mesenteric ischemia. The carcinoid syndrome is known for its cardiac involvement most well characterized by fibrous tissue deposits on the endocardium.(1,2) Case reports of coronary artery vasospasm have been previously described and hypothesized to be mediated by vasoactive amines and polypeptides synthesized by the tumor.(3-9) Intestinal ischemia is another reported complication of the carcinoid syndrome and is hypothesized to have a similar mechanism to that of the coronary vasospasm.(10-17) We have reviewed the literature and describe a case of coronary vasospasm and mesenteric ischemia in a patient on octreotide therapy. This is the first case in which we have identified concurrent coronary vasospasm and mesenteric ischemia in a patient with carcinoid disease.

Cognitive impairment associated with carcinoid syndrome.

OBJECTIVES: To evaluate the cognitive performance of patients with carcinoid syndrome (CS) compared with population norms and cancer patients with non-neuroendocrine (non-NET) liver metastases. BACKGROUND: The release of serotonin into the systemic circulation from metastatic small bowel neuroendocrine tumors (SB NET) causes CS. Many patients with CS followed in a multidisciplinary NET clinic seemed to exhibit a unique cognitive impairment. Because serotonin is known to influence a range of cognitive function, the question arouse as to whether cognitive impairment is another manifestation of CS. METHODS: Patients were recruited from the multidisciplinary NET and the hepatobilary cancer clinics at the cancer center. The CS group consisted of patients with proven SB NETs metastatic to liver; the cancer comparison group consisted of patients with liver metastases from non-NET cancer. All completed a self-reported cognitive questionnaire and a battery of 6 standardized neurocognitive tests. Both groups were compared to age/sex/educational-matched norms. RESULTS: Thirty-six patients with CS and 20 with non-NET metastases were enrolled. Patients with CS reported greater cognitive dysfunction in all cognitive domains than both norms and the comparison cancer group. On cognitive testing, patients with CS demonstrated weakness in initiation, processing speed, visual memory, cognitive efficiency, and delayed verbal recall compared with norms. Although the patients with non-NET cancer also demonstrated some cognitive dysfunction compared with norms, the patients with CS did significantly worse on delayed recall (P = 0.03) and marginally slower on speeded mental flexibility (P = 0.097) compared with patients with non-NET cancer. CONCLUSION: This study confirmed our clinical observation that patients with CS suffer from cognitive impairment that is different from the non-NET cancer group and population norms.

Clinical benefits of above-standard dose of octreotide LAR in patients with neuroendocrine tumors for control of carcinoid syndrome symptoms: a multicenter retrospective chart review study.

BACKGROUND: Octreotide LAR is used in patients for control of carcinoid syndrome (CS) and other symptoms of hormone hypersecretion. The aim of this study was to examine reasons for octreotide LAR dose escalation and observe CS symptom improvement in patients with neuroendocrine tumors (NETs) who underwent octreotide LAR dose escalation at three cancer referral centers. METHODS: Medical records for patients with diagnosis of carcinoid or pancreatic NET who had received one dose or more of octreotide LAR above 30 mg every 4 weeks from 2000 to 2012 were reviewed. Reasons for dose escalation and symptomatic outcomes were abstracted for each patient 3 months prior to and up to 12 months following the dose escalation. RESULTS: Of the evaluated 239 NET patients, 53% were male, mean age at first dose escalation was 60 years (standard deviation [SD]: 11 years), and mean time from octreotide LAR initiation to first dose escalation was 1.7 years (SD: 2.0 years). The primary reasons reported for dose escalation were carcinoid or hormonal syndrome (62%) or radiographic progression (28%). The most common dose changes at the first dose escalation were 40 mg every 4 weeks (71%) and 60 mg every 4 weeks (18%). Of 90 patients in whom flushing was reported prior to first dose escalation, 73 (81%) were reported to have experienced improvement or resolution of their symptoms following the dose escalation. Of 107 patients who were reported to have experienced diarrhea before the first dose escalation, 85 (79%) were reported to have experienced improvement or resolution after first dose escalation. CONCLUSION: The goal of improved symptom control is a common reason for dose escalation of octreotide LAR. This study suggests that escalation to above the standard dose of octreotide LAR of 30 mg every 4 weeks may result in improved CS symptom control.

[A 59-year-old patient with recurrent flushes and bland hepatic cyst]. / 59-jähriger Patient mit rezidivierendem Erröten bei blander Leberzyste.

A 59-year-old patient was admitted to hospital with recurrent flush symptoms and pathologically elevated 5-hydroxyindoleacetic acid (5-HIAA) levels in urine. A known cystic lesion of the liver which had been followed for years by ultrasound examinations and was regarded as a bland hepatic cyst was identified as a metastasis of a neuroendocrine neoplasm of the ileum. In two sequential surgical interventions the primary tumor with mesenteric lymph node metastases as well as the cystic liver metastasis could be resected. After surgical treatment an R1 situation at the mesenteric site and suspicious para-aortic lymph nodes remained. The long established treatment of factor-V Leiden mutation by anticoagulation with phenprocoumon was supplemented by deep subcutaneous injection of lanreotide autogel every 4 weeks. Currently, there is no evidence for progressive disease and the patient is without clinical signs of a carcinoid syndrome.

Anesthetic considerations and management of a patient with unsuspected carcinoid crisis during hepatic tumor resection.

Anesthetic management for massive blood loss in liver surgery concomitant with hemodynamic instability secondary to carcinoid crisis can be challenging in the perioperative setting. Hypotension, diarrhea, facial flushing, bronchospasm, and tricuspid and pulmonic valvular diseases are the common manifestations of carcinoid syndrome. This report illustrates the importance of early recognition and treatment for signs and symptoms of carcinoid syndrome not only in the preoperative setting but also in the intraoperative phase to prevent undue cardiovascular collapse.

Health care resource use and costs among patients with carcinoid syndrome in France: Analysis of the National Health Insurance Database.

OBJECTIVES: Carcinoid syndrome (CS) develops in approximately 20% of patients with neuroendocrine tumours (NET). This study described healthcare resource utilization and its associated costs among patients with NET and CS, using the French national health care data system. METHODS: Patients were included if they had a hospital stay associated with the code E34.0 "CS" and at least one delivery of a somatostatin analogue (SSA) between 01/01/2012 and 31/12/2016. The end of the analysis was either 31/12/2017 or the date of death, whichever occurred first. Mean overall costs were described by item of expenditure and by periods. RESULTS: 646 patients were included: 64yo, 55% men, 64% and 15% had NET from the small-intestine or lung, respectively. Among them, 309 patients were incident and 271 died during the study period. Mean overall cost per person per month (PPPM) was €2,892: €3,273 for the first year following diagnosis, €2,574 in "middle-years" and €5,039 within the year preceding death. The two most costly expenditure items were drugs (€1,695 PPPM) and hospital stays (€870 PPPM). CONCLUSION: The first year following diagnosis and the year preceding death are the two periods representing the highest costs for CS care in France. Successful disease management may contribute to lower costs in the intermediate period.

Efficacy, safety and unmet needs of evolving medical treatments for carcinoid syndrome.

This review reports on the currently available medical treatment options for the control of symptoms due to carcinoid syndrome in patients with neuroendocrine tumors. The efficacy and adverse events (AEs) of approved drugs such as somatostatin analogues (SSA), telotristat ethyl (TE) and interferon-alpha, are reviewed. Somatostatin analogues remain the standard treatment of carcinoid syndrome based on the high expression of somatostatin receptors and the resulting inhibition of secretion of bioactive compounds; their use is associated with relatively mild AEs, involving mainly the gastrointestinal system, and being usually transient. Although dose escalation of SSA remains an unapproved option, it is clinically implemented to alleviate symptoms in refractory carcinoid syndrome and supported by the most recent guidelines. The side effects associated with the increased dose are in general mild and consistent with standard dose of SSA. Telotristat ethyl, an oral inhibitor of tryptophan hydroxylase, the rate-limiting enzyme in serotonin biosynthesis, represents a rather novel innovative treatment option in patients with carcinoid syndrome suffering from diarrhea and complements the standard therapy of SSA. Given the low toxicity profile, TE may be considered an early add-on treatment to SSA in patients with uncontrolled carcinoid syndrome. However, further prolonged follow-up of patients treated with TE may be needed to exclude potential AEs, such as liver toxicity or depressed mood, in patients with long-term treatment. Interferon alpha is a cytokine with direct inhibitory effect on hormone secretion and tumor cell proliferation and an approved therapy in carcinoid syndrome but is associated with significant AEs in the majority of the patients requiring frequently dose reduction. The finding of a more favorable tolerability of pegylated interferon needs to be confirmed in a prospective study.

A prospective study of carcinoid crisis with no perioperative octreotide.

BACKGROUND: Carcinoid crises, defined as the sudden onset of hemodynamic instability in patients with neuroendocrine tumors undergoing operation, are associated with significantly increased risk of postoperative complications. Octreotide has been used prophylactically to reduce crisis rates as well as therapeutically to treat crises that still occur. However, studies using octreotide still report crisis rates of 3.4% to 35%, leading to the questioning of its efficacy. METHODS: Patients with neuroendocrine tumors undergoing operation between 2017 to 2020 with no perioperative octreotide were prospectively studied. Clinicopathologic data were compared by χ2 test for discrete variables and by Mann-Whitney U test for continuous variables. RESULTS: One hundred and seventy-one patients underwent 195 operations. Crisis was documented in 49 operations (25%), with a mean duration of 3 minutes. Crisis was more likely to occur in patients with small bowel primary tumors (P = .012), older age (P = .015), and carcinoid syndrome (P < .001). Those with crises were more likely to have major postoperative complications (P = .003). CONCLUSION: Completely eliminating perioperative octreotide resulted in neither increased rate nor duration compared with previous studies using octreotide. We conclude perioperative octreotide use may be safely stopped, owing to inefficacy, though the need for an effective medication is clear given continued higher rates of complications.

Recent Advances in the Diagnosis and Management of Carcinoid Syndrome.

Carcinoid syndrome, a paraneoplastic condition linked with the release of multiple humoral factors, affects around 30-40% of patients with well-differentiated neuroendocrine tumours. Carcinoid syndrome has a major and unfavourable impact on patients' quality of life; it raises costs when compared to non-functioning neuroendocrine tumours; and it causes patients' lifestyles to alter, such as food, job, physical activity, and social life. Somatostatin analogues have been the first-line therapy for individuals with neuroendocrine tumours and carcinoid disease for decades. While these drugs give considerable relief from carcinoid syndrome symptoms, clinical progression is unavoidable, necessitating further research into newer treatment measures. Carcinoid tumours are sometimes difficult to diagnose because of their vague or nonspecific symptoms. There have been several advancements in all aspects of carcinoid syndrome, as well as novel therapeutics, in the previous few years. New epidemiological studies show that it is becoming more common; increasing insights into the pathogenesis of its various clinical manifestations and its natural history: definition of prognostic factors; new methods to verify its presence; the development of new drugs to treat its various manifestations, both initially and in somatostatin-refractory cases; and an increased understanding of the pathogenesis, natural history, and management of the disease. An all language literature search was conducted on MEDLINE, COCHRANE, EMBASE, and Google Scholar till November 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: "Recent advances", "Carcinoid syndrome", "Neuroendocrine Neoplasms" and "Carcinoid heart disease". We comprehensively reviewed the literature on the pathogenesis, clinical features, and newer treatment modalities for Carcinoid Syndrome. Recent advancements in research and management have resulted from advances in our understanding of the aetiology of carcinoid syndrome. The development of molecular indicators of aggressiveness improved serum tumour markers, and the molecular aetiology of carcinoid heart disease are all possible because of advances in molecular biology. We conducted a comprehensive review to update knowledge regarding the pathophysiology, diagnostic protocols, and current and newer treatments for carcinoid syndrome, which presently requires a multidisciplinary approach, due to the complexity of the illness's aetiology, diagnosis, and therapy.

Arterial function, biomarkers, carcinoid syndrome and carcinoid heart disease in patients with small intestinal neuroendocrine tumours.

PURPOSE: Carcinoid heart disease (CHD) is a life-threatening complication of carcinoid syndrome (CS) characterised by tricuspid regurgitation (TR). However, there is an unmet need for earlier diagnosis of CHD. We cross-sectionally assessed the prevalence and potential predictive or diagnostic markers for CS and CHD in a contemporary cohort of patients with small intestinal neuroendocrine tumours (SI-NETs). METHODS: Biochemical characteristics, hepatic tumour load, measures of arterial and endothelial function, atherosclerosis, and transthoracic echocardiography were analysed in a prospective cross-sectional setting. RESULTS: Among the 65 patients studied, 29 (45%) had CS (CS+ ), and 3 (5%) CHD. CS+ was characterised by significantly higher hepatic tumour load, S-5-HIAA and fP-CgA, higher frequency of diarrhoea and flushing, and more frequent PRRT compared to CS- (for all, P < 0.05). Central systolic, central mean, and central end-systolic blood pressures were significantly higher in CS+ than in CS- (for all, P < 0.05). Subjects with grades 2-4 TR had higher hepatic tumour burden, fP-CgA, and S-5-HIAA compared to those with grades 0-1 TR, but measures of vascular function did not differ. fP-CgA (P = 0.017) and S-5-HIAA (P = 0.019) but not proBNP increased significantly according to the severity of TR. CONCLUSION: Although CS is common, the prevalence of CHD was found to be lower in a contemporary cohort of SI-NET patients than previously anticipated. Measures of arterial or endothelial function or carotid atherosclerosis do not identify subjects with mild TR. Echocardiography remains the most sensitive means to diagnose CHD in CS patients with high tumour burden and elevated CgA and 5-HIAA.

Pellagra: a review with emphasis on photosensitivity.

Niacin has recently been demonstrated to lower blood pressure in hypertensive patients and to reduce cardiovascular events when combined with a statin. As a consequence, niacin has been elevated from being of historical interest as the treatment for pellagra, to being a compound with possible relevance to contemporary therapeutics. In spite of this, niacin deficiency leading to pellagra continues to be a health problem in some countries. Characterized by an exposed-site hyperpigmented dermatitis, pellagra is generally accepted to have been the first photosensitivity syndrome described. At its worst, pellagra manifests as one of the most striking examples of systemic photosensitivity. This is the only photosensitivity syndrome where death is included as a cardinal clinical feature (the often quoted four 'Ds': dermatitis, diarrhoea, dementia and death). However, the pathogenetic mechanism for the photosensitivity caused by niacin deficiency has yet to be determined. This review seeks to update the classification and phenotypic characterization of the various forms of niacin-deficient photosensitivity. Previous speculation about possible mechanisms for the pathogenesis of photosensitivity due to niacin deficiency is reviewed in the context of advances in the understanding of the photochemical basis of photosensitivity reactions. The review concludes by highlighting research required to advance the understanding of this photosensitivity syndrome.