3 DISCUSSION
Black esophagus, also known as ANE, was first described by Goldenberg et al. in 1990 (1), and gained prominence after a series of cases were reported in 2007 (2). AEN has remained a rare diagnosis with an estimated prevalence of up to 0.28% (3,4). It has an endoscopic finding characterized by diffuse, circumferential black discoloration of the mucosa that affects the distal part of the esophagus and stops abruptly at the gastroesophageal junction (1-4,7,10).
Though the exact etiology of the disease remains unclear, it is presumed to be multifactorial with ischemia, impaired intrinsic mucosal barriers, and massive reflux of gastric contents that acutely exceeds the protective and regenerative properties of vulnerable esophageal mucosa enabling both ischemic and chemical injury of the esophagus (3,4,8,11-13). Chronic predisposing conditions and poor nutritional status may also contribute to decreased mucosal buffering and may potentiate the mechanisms by which esophageal necrosis is progressed.
Diagnosis of AEN is based on endoscopic findings which consist of a circumferentially black-appearing esophageal mucosa that abruptly ends at the gastroesophageal junction and transitions to normal gastric mucosa (1-4,7,10). Biopsy is supportive and obtained to exclude other etiologies, but is not required to establish the diagnosis (3,4). Patients are typically older males with multiple medical comorbidities, which increase the likelihood of AEN (2-4). Demographically, hyperglycemia is seen in almost 90% of patients with this condition (14,15). Moreover, disease associations include vascular compromise, hypertension, chronic kidney disease, malignancy, malnourishment, gastric outlet obstruction, and in this case, diabetes mellitus and alcohol abuse (3,4). The clinical presentation is remarkable for upper gastrointestinal bleeding, with most patients presenting with hematemesis or melena, comparable to our case (3,4). Other symptoms may include abdominal pain, nausea, vomiting, dysphagia, fever, and syncope (3,4). The patient presented with abdominal pain and nausea. Laboratory findings are nonspecific, but it has been reported that associated laboratory abnormalities may include anemia, leukocytosis, and hyperlactatemia (3,4), all of which are comparable to the patient.
There is no specific therapy for AEN. Management of AEN should be directed at correcting the underlying medical condition and protective care with hemodynamic resuscitation, total parenteral nutrition, and the administration of antacid therapy with aggressive intravenous proton pump inhibitors (3,4). Enteral feeding is not recommended because of the risk of perforation unless there is persistent vomiting (3,4,9). Moreover, prophylactic antibiotics are not necessary. The decision to initiate antimicrobial therapy should be individualized based on clinical and objective findings of serious infection (3,4,9,16). The patient presented no sign of infection. The most common long-term sequela of AEN is stricture formation, which can complicate up to 10% of all cases (3,4,9). No stricture formation was shown in our case on follow-up EGD.
The correlation between DKA and AEN has been described in the literature (14,17-23). DKA has been reported to be one of the most common triggering events for AEN (3,4,9). Although the precise mechanism remains unknown, several pathogenic mechanisms may possibly be implicated. The presence of long-standing diabetes mellitus predisposes the patient to the development of atherosclerosis leading to an increased risk of ischemia (3,4,14,19,24,25). It has been suggested that poor nutritional status with hemodynamic instability, and hyperglycemia in DKA can lead to poor vascular flow and an impaired mucosal barrier from corrosive injury of gastric contents (3,4,8,14,19,24,25). Moreover, gastric stasis, which can occur in the absence of neuropathy during DAK, can induce gastroesophageal reflux by which esophageal necrosis is accelerated (3,4,19). DKA can also result in profound osmotic diuresis and fluid loss leading to hypoperfusion of the distal esophagus (3,4,14,18).
In summary, we presented a case of AEN complicating diabetic ketoacidosis. Though AEN remains a rare cause of upper gastrointestinal bleeding, it is a potentially life-threatening condition. Notably, up to 9% of patients with DKA have evidence of upper gastrointestinal bleeding, but less than one-third of those undergo endoscopy to determine the underlying cause (10). Therefore, a clinician should be aware of AEN as a potential cause of upper gastrointestinal bleeding when faced with an elderly, possibly poorly controlled diabetic patient or when additional significant comorbidities are present.