Design and Clinical Evaluation of a Novel Low-Glucose Prediction Algorithm with Mini-Dose Stable Glucagon Delivery in Post-Bariatric Hypoglycemia

Postbariatric surgery hypoglycemia: Nutritional, pharmacological and surgical perspectives

Post-bariatric hypoglycaemia (PBH) is a metabolic complication of bariatric surgery (BS), consisting of low post-prandial glucose levels in patients having undergone bariatric procedures. While BS is currently the most effective and relatively safe treatment for obesity and its complications, the development of PBH can significantly impact patients' quality of life and mental health. The diagnosis of PBH is still challenging, considering the lack of definitive and reliable diagnostic tools, and the fact that this condition is frequently asymptomatic. However, PBH's prevalence is alarming, involving up to 88% of the post-bariatric population, depending on the diagnostic tool, and this may be underestimated. Given the prevalence of obesity soaring, and an increasing number of bariatric procedures being performed, it is crucial that physicians are skilled to diagnose PBH and promptly treat patients suffering from it. While the milestone of managing this condition is nutritional therapy, growing evidence suggests that old and new pharmacological approaches may be adopted as adjunct therapies for managing this complex condition.

Dasiglucagon Treatment for Postprandial Hypoglycemia After Gastric Bypass: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVE

Postbariatric hypoglycemia affects >50% of individuals who have undergone Roux-en-Y gastric bypass surgery. Despite the often debilitating nature of this complication, existing treatment options are limited and often inefficient. Dasiglucagon is a stable glucagon analog available in a ready-to-use formulation and was recently shown to mitigate postbariatric hypoglycemia in experimental settings. Here, we aimed to evaluate the hypoglycemic hindering potential of dasiglucagon in an outpatient trial.

RESEARCH DESIGN AND METHODS

We conducted a randomized, double-blind, placebo-controlled, crossover, proof-of-concept study at the Center for Clinical Metabolic Research at Gentofte Hospital in Denmark. The study included 24 individuals who had undergone Roux-en-Y gastric bypass surgery (n = 23 women) with continuous glucose monitor-verified postbariatric hypoglycemia (≥15 min at <3.9 mmol/L three or more times per week) randomly assigned to two treatment periods of 4 weeks of self-administered subcutaneous dasiglucagon at 120 μg or placebo. The primary and key secondary outcomes were continuous glucose monitor-captured percentage of time in level 1 and 2 hypoglycemia (<3.9 and <3.0 mmol/L), respectively.

RESULTS

Compared with placebo, treatment with dasiglucagon significantly reduced time in level 1 hypoglycemia by 33% (-1.2 percentage points; 95% CI -2.0 to -0.5; P = 0.002) and time in level 2 hypoglycemia by 54% (-0.4 percentage points; 95% CI -0.6 to -0.2; P < 0.0001). Furthermore, dasiglucagon corrected hypoglycemia within 15 min in 401 of 412 self-administrations, compared with 104 of 357 placebo self-administrations (97.3% vs. 29.1% correction of hypoglycemia rate; P < 0.001). Dasiglucagon was generally well tolerated, with mostly mild to moderate adverse events of nausea.

CONCLUSIONS

Compared with placebo, 4 weeks of self-administered dasiglucagon effectively reduced clinically relevant hypoglycemia in individuals who had undergone Roux-en-Y gastric bypass surgery.

New Developments in Glucagon Treatment for Hypoglycemia

Glucagon is essential for endogenous glucose regulation along with the paired hormone, insulin. Unlike insulin, pharmaceutical use of glucagon has been limited due to the unstable nature of the peptide. Glucagon has the potential to address hypoglycemia as a major limiting factor in the treatment of diabetes, which remains very common in the type 1 and type 2 diabetes. Recent developments are poised to change this paradigm and expand the use of glucagon for people with diabetes. Glucagon emergency kits have major limitations for their use in treating severe hypoglycemia. A complicated reconstitution and injection process often results in incomplete or aborted administration. New preparations include intranasal glucagon with an easy-to-use and needle-free nasal applicator as well as two stable liquid formulations in pre-filled injection devices. These may ease the burden of severe hypoglycemia treatment. The liquid preparations may also have a role in the treatment of non-severe hypoglycemia. Despite potential benefits of expanded use of glucagon, undesirable side effects (nausea, vomiting), cost, and complexity of adding another medication may limit real-world use. Additionally, more long-term safety and outcome data are needed before widespread, frequent use of glucagon is recommended by providers.

Dasiglucagon Effectively Mitigates Postbariatric Postprandial Hypoglycemia: A Randomized, Double-Blind, Placebo-Controlled, Crossover Trial

OBJECTIVE

To investigate the efficacy and safety of dasiglucagon, a novel stable glucagon analog in a liquid formulation, in Roux-en-Y gastric bypass (RYGB)-operated individuals suffering from postbariatric hypoglycemia (PBH).

RESEARCH DESIGN AND METHODS

In a randomized, double-blind, placebo-controlled, crossover trial, 10 RYGB-operated participants with continuous glucose monitoring-verified PBH were randomly assigned to 3 trial days, each consisting of a 240-min standardized liquid mixed-meal test with the subcutaneous injection of placebo or 80 μg or 200 μg dasiglucagon.

RESULTS

Compared with placebo, treatment with both 80 and 200 μg dasiglucagon raised nadir plasma glucose (PG) (placebo: 3.0 ± 0.2 mmol/L [mean ± SEM]; 80 μg dasiglucagon: 3.9 ± 0.3 mmol/L, P = 0.002; 200 μg dasiglucagon: 4.5 ± 0.2 mmol/L, P = 0.0002) and reduced time in hypoglycemia (PG <3.9 mmol/L) by 70.0 min (P = 0.030 and P = 0.008).

CONCLUSIONS

Single-dose administration of dasiglucagon effectively mitigated postprandial hypoglycemia.

Digital Solutions to Diagnose and Manage Postbariatric Hypoglycemia

Postbariatric hypoglycemia (PBH) is an increasingly recognized late metabolic complication of bariatric surgery, characterized by low blood glucose levels 1–3 h after a meal, particularly if the meal contains rapid-acting carbohydrates. PBH can often be effectively managed through appropriate nutritional measures, which remain the cornerstone treatment today. However, their implementation in daily life continues to challenge both patients and health care providers. Emerging digital technologies may allow for more informed and improved decision-making through better access to relevant data to manage glucose levels in PBH. Examples include applications for automated food analysis from meal images, digital receipts of purchased food items or integrated platforms allowing the connection of continuously measured glucose with food and other health-related data. The resulting multi-dimensional data can be processed with artificial intelligence systems to develop prediction algorithms and decision support systems with the aim of improving glucose control, safety, and quality of life of PBH patients. Digital innovations, however, face trade-offs between user burden vs. amount and quality of data. Further challenges to their development are regulatory non-compliance regarding data ownership of the platforms acquiring the required data, as well as user privacy concerns and compliance with regulatory requirements. Through navigating these trade-offs, digital solutions could significantly contribute to improving the management of PBH.

Glycemic Patterns Are Distinct in Post-Bariatric Hypoglycemia After Gastric Bypass (PBH-RYGB)

CONTEXT

Severe hypoglycemia with neuroglycopenia, termed post-bariatric hypoglycemia (PBH). typically occurs postprandially, but it is also reported after activity or mid-nocturnally.

OBJECTIVE

To quantify glycemia, glycemic variability, and magnitude/duration of low sensor glucose (SG) values in patients with PBH after Roux-en-Y gastric bypass (PBH-RYGB).

METHODS

This retrospective analysis of data from an academic medical center included individuals with PBH-RYGB (n = 40), reactive hypoglycemia without gastrointestinal surgery (Non-Surg Hypo, n = 20), prediabetes (Pre-DM, n = 14), newly diagnosed T2D (n = 5), and healthy controls (HC, n = 38). Masked continuous glucose monitoring (Dexcom G4) was used to assess patterns over 24 hours, daytime (6 am-midnight) and nighttime (midnight-6 am). Prespecified measures included mean and median SG, variability, and percent time at thresholds of sensor glucose.

RESULTS

Mean and median SG were similar for PBH-RYGB and HC (mean: 99.8 ± 18.6 vs 96.9 ± 10.2 mg/dL; median: 93.0 ± 14.8 vs 94.5 ± 7.4 mg/dL). PBH-RYGB had a higher coefficient of variation (27.3 ± 6.8 vs 17.9 ± 2.4%, P < 0.0001) and range (154.5 ± 50.4 vs 112.0 ± 26.7 mg/dL, P < 0.0001). Nadir was lowest in PBH-RYGB (42.5 ± 3.7 vs HC 49.0 ± 11.9 mg/dL, P = 0.0046), with >2-fold greater time with SG < 70 mg/dL vs HC (7.7 ± 8.4 vs 3.2 ± 4.1%, P = 0.0013); these differences were greater at night (12.6 ± 16.9 vs 1.0 ± 1.5%, P < 0.0001). Non-Surg Hypo also had 4-fold greater time with SG < 70 at night vs HC (SG < 70: 4.0 ± 5.9% vs 1.0 ± 1.5%), but glycemic variability was not increased.

CONCLUSION

Patients with PBH-RYGB experience higher glycemic variability and frequency of SG < 70 compared to HC, especially at night. These data suggest that additional pathophysiologic mechanisms beyond prandial changes contribute to PBH.

Hyperinsulinemic hypoglycemia in children and adolescents: Recent advances in understanding of pathophysiology and management

Hyperinsulinemic hypoglycemia (HH) is characterized by unregulated insulin release, leading to persistently low blood glucose concentrations with lack of alternative fuels, which increases the risk of neurological damage in these patients. It is the most common cause of persistent and recurrent hypoglycemia in the neonatal period. HH may be primary, Congenital HH (CHH), when it is associated with variants in a number of genes implicated in pancreatic development and function. Alterations in fifteen genes have been recognized to date, being some of the most recently identified mutations in genes HK1, PGM1, PMM2, CACNA1D, FOXA2 and EIF2S3. Alternatively, HH can be secondary when associated with syndromes, intra-uterine growth restriction, maternal diabetes, birth asphyxia, following gastrointestinal surgery, amongst other causes. CHH can be histologically characterized into three groups: diffuse, focal or atypical. Diffuse and focal forms can be determined by scanning using fluorine-18 dihydroxyphenylalanine-positron emission tomography. Newer and improved isotopes are currently in development to provide increased diagnostic accuracy in identifying lesions and performing successful surgical resection with the ultimate aim of curing the condition. Rapid diagnostics and innovative methods of management, including a wider range of treatment options, have resulted in a reduction in co-morbidities associated with HH with improved quality of life and long-term outcomes. Potential future developments in the management of this condition as well as pathways to transition of the care of these highly vulnerable children into adulthood will also be discussed.

Guidelines for gastrostomy tube placement and enteral nutrition in patients with severe, refractory hypoglycemia after gastric bypass

BACKGROUND

Postbariatric hypoglycemia (PBH) affects up to 38% of Roux-en-Y gastric bypass (RYGB) patients. Severe cases are refractory to diet and medications. Surgical treatments including bypass reversal and pancreatectomy are highly morbid and hypoglycemia often recurs. We have developed a highly effective method of treatment by which enteral nutrition administered through a gastrostomy (G) tube placed in the remnant stomach replaces oral diet: if done correctly this reverses hyperinsulinemia and hypoglycemia, yielding substantial health and quality of life benefits for severely affected patients.

OBJECTIVES

To provide clinical guidelines for placement of a G-tube to treat postRYGB hypoglycemia, including candidate selection, preoperative evaluation, surgical considerations, and post-RYGB management.

SETTING

Stanford University Hospital and Clinics.

METHODS

Based on our relatively large experience with placing and managing G-tubes for PBH treatment, an interdisciplinary task force developed guidelines for practitioners.

RESULTS

A team approach (endocrinologist, dietitian, surgeon, psychologist) is recommended. Appropriate candidates have a history of RYGB, severe hypoglycemia refractory to medical-nutrition therapy, and significantly affected quality of life. Preoperative requirements include education and expectation setting, determination of initial enteral feeding program, and establishing service with a home enteral provider. Close postoperative follow-up is needed to ensure success and may require adjustments in formula and mode/rate of delivery to optimize tolerance and meet nutritional goals. G-tube nutrition must fully replace oral nutrition to prevent hypoglycemia.

CONCLUSIONS

G-tube placement in the remnant stomach represents a relatively well-tolerated and effective treatment for severe, refractory hypoglycemia after RYGB.

Safety, efficacy and pharmacokinetics of repeat subcutaneous dosing of avexitide (exendin 9-39) for treatment of post-bariatric hypoglycaemia

AIM

To evaluate the safety, efficacy and pharmacokinetics of repeat dosing of two formulations of subcutaneous (SC) avexitide (exendin 9-39) in patients with post-bariatric hypoglycaemia (PBH).

METHODS

In this phase 2, multiple-ascending-dose study conducted at Stanford University, 19 women with PBH underwent a baseline oral glucose tolerance test (OGTT), with metabolic and symptomatic assessments. Fourteen were then sequentially assigned to receive one of four ascending-dose levels of twice-daily lyophilized (Lyo) avexitide by SC injection for 3 days. On the basis of safety, efficacy and tolerability, five additional participants then received a novel liquid formulation (Liq) of avexitide by SC injection at a fixed dose of 30 mg twice daily for 3 days. All 19 participants underwent a repeat OGTT on day 3 of dosing to quantify metabolic, symptomatic and pharmacokinetic responses.

RESULTS

Treatment with Lyo avexitide reduced the magnitude of symptomatic hyperinsulinaemic hypoglycaemia at all dose levels, with dose-dependent improvements in glucose nadir, insulin peak and symptom score; doses ≥20 mg twice daily did not require glycaemic rescue (administered at glucose <2.8 mmol/L). Participants receiving Liq avexitide 30 mg twice daily did not require any glycaemic rescue, and on average achieved a 47% increase in glucose nadir, a 67% reduction in peak insulin, and a 47% reduction in overall symptom score. Equivalent doses of Liq versus Lyo avexitide yielded higher and more sustained plasma concentrations. Both formulations were well tolerated.

CONCLUSIONS

In patients with PBH, twice-daily administration of SC avexitide effectively raised the glucose nadir and prevented severe hypoglycaemia requiring rescue intervention. Avexitide may represent a viable therapy for PBH.

A Randomized, Placebo-Controlled Double-Blind Trial of a Closed-Loop Glucagon System for Postbariatric Hypoglycemia

BACKGROUND

Postbariatric hypoglycemia (PBH) can threaten safety and reduce quality of life. Current therapies are incompletely effective.

METHODS

Patients with PBH were enrolled in a double-blind, placebo-controlled, crossover trial to evaluate a closed-loop glucose-responsive automated glucagon delivery system designed to reduce severe hypoglycemia. A hypoglycemia detection and mitigation algorithm was embedded in the artificial pancreas system connected to a continuous glucose monitor (CGM, Dexcom) driving a patch infusion pump (Insulet) filled with liquid investigational glucagon (Xeris) or placebo (vehicle). Sensor/plasma glucose responses to mixed meal were assessed during 2 study visits. The system delivered up to 2 doses of study drug (300/150 μg glucagon or equal-volume vehicle) if triggered by the algorithm. Rescue dextrose was given for plasma glucose <55 mg/dL or neuroglycopenia.

RESULTS

Twelve participants (11 females/1 male, age 52 ± 2, 8 ± 1 years postsurgery, mean ± SEM) completed all visits. Predictive hypoglycemia alerts prompted automated drug delivery postmeal, when sensor glucose was 114 ± 7 vs 121 ± 5 mg/dL (P = .39). Seven participants required rescue glucose after vehicle but not glucagon (P = .008). Five participants had severe hypoglycemia (<55 mg/dL) after vehicle but not glucagon (P = .03). Nadir plasma glucose was higher with glucagon vs vehicle (67 ± 3 vs 59 ± 2 mg/dL, P = .004). Plasma glucagon rose after glucagon delivery (1231 ± 187 vs 16 ± 1 pg/mL at 30 minutes, P = .001). No rebound hyperglycemia occurred. Transient infusion site discomfort was reported with both glucagon (n = 11/12) and vehicle (n = 10/12). No other adverse events were observed.

CONCLUSION

A CGM-guided closed-loop rescue system can detect imminent hypoglycemia and deliver glucagon, reducing severe hypoglycemia in PBH.

CLINICAL TRIALS REGISTRATION

NCT03255629.

Hypoglycemia After Upper Gastrointestinal Surgery: Clinical Approach to Assessment, Diagnosis, and Treatment

CONTEXT

Post-bariatric hypoglycemia (PBH) is an increasingly encountered complication of upper gastrointestinal surgery; the prevalence of this condition is anticipated to rise given yearly increases in bariatric surgical procedures. While PBH is incompletely understood, there is a growing body of research describing the associated factors, mechanisms, and treatment approaches for this condition.

EVIDENCE ACQUISITION

Data are integrated and summarized from studies of individuals affected by PBH and hypoglycemia following upper gastrointestinal surgery obtained from PubMed searches (1990-2020).

EVIDENCE SYNTHESIS

Information addressing etiology, incidence/prevalence, clinical characteristics, assessment, and treatment were reviewed and synthesized for the practicing physician. Literature reports were supplemented by clinical experience as indicated, when published data were not available.

CONCLUSION

PBH can be life-altering and severe for a subset of individuals. Given the chronic nature of this condition, and sequelae of both acute and recurrent episodes, increasing provider awareness of both the condition and associated risk factors is critical for assessment, prompt diagnosis, treatment, and preoperative identification of individuals at risk.

Management of Diabetes in Patients Undergoing Bariatric Surgery

PURPOSE OF REVIEW

The number of bariatric surgeries for patients with type 1 or type 2 diabetes continues to grow. Clinicians are challenged to choose therapies that reach glycemic targets without inducing adverse effects in post-bariatric patients without published guidelines. This review evaluates data supporting the best strategies for diabetes management in patients undergoing bariatric surgery.

RECENT FINDINGS

Though few clinical trials have evaluated the safety and effectiveness of different glucose-lowering therapies following bariatric surgery, remission of diabetes or reduced medications is an established benefit of bariatric surgery. Adverse events including diabetic ketoacidosis in post-bariatric patients on sodium-glucose co-transporter 2 (SGLT2) inhibitors or inadequate insulin have been reported in patient's with both type 1 and type 2 diabetes. Metformin, glucagon-like peptide-1 (GLP-1) agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, SGLT2 inhibitors, insulin, and sulfonylureas have been used successfully in the perioperative period for other surgeries and guidelines recommend adjusting the doses of these medications especially in the perioperative period. Clinicians should favor weight-neutral or weight-loss promoting therapies in post-bariatric surgery patients such as medical nutrition therapy, metformin, GLP-1 agonists, SGLT2 inhibitors, and DPP-4 inhibitors.

Novel Preparations of Glucagon for the Prevention and Treatment of Hypoglycemia

PURPOSE OF REVIEW

New more stable formulations of glucagon have recently become available, and these provide an opportunity to expand the clinical roles of this hormone in the prevention and management of insulin-induced hypoglycemia. This is applicable in type 1 diabetes, hyperinsulinism, and alimentary hypoglycemia. The aim of this review is to describe these new formulations of glucagon and to provide an overview of current and future therapeutic opportunities that these may provide.

RECENT FINDINGS

Four main categories of glucagon formulation have been studied: intranasal glucagon, biochaperone glucagon, dasiglucagon, and non-aqueous soluble glucagon. All four have demonstrated similar glycemic responses to standard glucagon formulations when administered during hypoglycemia. In addition, potential roles of these formulations in the management of congenital hyperinsulinism, alimentary hypoglycemia, and exercise-induced hypoglycemia in type 1 diabetes have been described. As our experience with newer glucagon preparations increases, the role of glucagon is likely to expand beyond the emergency use that this medication has been limited to in the past. The innovations described in this review likely represent early examples of a pending large repertoire of indications for stable glucagon.

Postprandial hypoglycaemia after Roux-en-Y gastric bypass and the effects of acarbose, sitagliptin, verapamil, liraglutide and pasireotide

AIM

To investigate the effects of acarbose, sitagliptin, verapamil, liraglutide and pasireotide on post-bariatric hypoglycaemia (PBH) after Roux-en-Y gastric bypass.

MATERIALS AND METHODS

In a randomized crossover study, 11 women who had undergone Roux-en-Y gastric bypass and had documented hypoglycaemia were each evaluated during a baseline period without treatment and during five treatment periods with the following interventions: acarbose 50 mg for 1 week, sitagliptin 100 mg for 1 week, verapamil 120 mg for 1 week, liraglutide 1.2 mg for 3 weeks and pasireotide 300 μg as a single dose. Treatment effects were evaluated by a mixed-meal tolerance test (MMTT) and, for all treatment periods except pasireotide, by 6 days of continuous glucose monitoring (CGM).

RESULTS

Treatment with acarbose and treatment with pasireotide both significantly lifted nadir glucose levels (mean ± SEM 3.9 ± 0.2 and 7.9 ± 0.4 vs 3.4 ± 0.2; P < .03) and reduced time in hypoglycaemia during the MMTTs. Acarbose reduced peak glucose levels and time in hyperglycaemia, whereas pasireotide greatly increased both variables. Acarbose and pasireotide reduced insulin and C-peptide levels, and pasireotide also diminished glucagon-like peptide-1 levels. Sitagliptin lowered nadir glucose values, while verapamil and liraglutide had no effect on hypoglycaemia. During the CGM periods, the treatments had no impact on hypoglycaemia, whereas acarbose and liraglutide reduced hyperglycaemia and glycaemic variability.

CONCLUSIONS

In an experimental setting, treatment with acarbose and pasireotide reduced PBH. Acarbose appears to have an overall glucose-stabilizing effect, whereas pasireotide leads to increased and sustained hyperglycaemia.

Postprandial hypoglycemia after gastric bypass surgery: from pathogenesis to diagnosis and treatment

PURPOSE OF REVIEW

The Roux-en-Y gastric bypass surgery (RYGB) improves glucose control in majority of patients with type 2 diabetes. However, a minority group of individuals develop a life-threatening complication of hyperinsulinemic hypoglycemia. The goal of this review is to identify underlying mechanisms by which RYGB cause hypoglycemia and describe pathogenesis-driven strategies to diagnose and treat this condition.

RECENT FINDINGS

Gastric bypass leads to higher and earlier peak levels of glucose and lower nadir glucose after eating along with larger insulin and glucagon-like peptide 1 (GLP-1) secretion, resetting the balance between glucose appearance and clearance after this procedure. These weight-loss independent glycemic effects of RYGB have been attributed to changes in ingested glucose appearance as a result of rapid nutrient emptying from stomach pouch to the intestine and increased glucose clearance as a result of prandial hyperinsulinemia. The exaggerated effect of RYGB on postmeal glucose metabolism is a syndrome of postprandial hyperinsulinemic hypoglycemia manifesting in a group of individuals several years after this surgery. Affected patients have larger systemic appearance of ingested glucose and greater postmeal secretion of insulin and GLP-1 compared to those with history of RYGB without symptomatic hypoglycemia. Current evidence supporting a multifactorial model of glucose dysregulation among patients with hypoglycemia will be highlighted in this review.

SUMMARY

Hypoglycemia after RYGB is a life-threatening condition and likely represents the extreme glycemic phenotype of this procedure. Diagnosis is challenging and treatment options are limited.

Hypoglycemia After Gastric Bypass Surgery: Current Concepts and Controversies

CONTEXT

Hypoglycemia, occurring after bariatric and other forms of upper gastrointestinal surgery, is increasingly encountered by clinical endocrinologists. The true frequency of this condition remains uncertain, due, in part, to differences in the diagnostic criteria and in the affected populations, as well as relative lack of patient and physician awareness and understanding of this condition. Postbariatric hypoglycemia can be severe and disabling for some patients, with neuroglycopenia (altered cognition, seizures, and loss of consciousness) leading to falls, motor vehicle accidents, and job and income loss. Moreover, repeated episodes of hypoglycemia can result in hypoglycemia unawareness, further impairing safety and requiring the assistance of others to treat hypoglycemia.

OBJECTIVE

In this review, we summarize and integrate data from studies of patients affected by hypoglycemia after Roux-en-Y gastric bypass (RYGB) surgery, obtained from PubMed searches (1990 to 2017) and reference searches of relevant retrieved articles. Whereas hypoglycemia can also be observed after sleeve gastrectomy and fundoplication, this review is focused on post-RYGB, given the greater body of published clinical studies at present.

OUTCOME MEASURES

Data addressing specific aspects of diagnosis, pathophysiology, and treatment were reviewed by the authors; when not available, the authors have provided opinions based on clinical experience with this challenging condition.

CONCLUSIONS

Hypoglycemia, occurring after gastric bypass surgery, is challenging for patients and physicians alike. This review provides a systematic approach to diagnosis and treatment based on the underlying pathophysiology.