Hereditary mucoepithelial dysplasia (HMD), or simply mucoepithelial dysplasia, is a rare autosomal dominant multiepithelial disorder causing systemic maldevelopment of the epithelia and mucous membranes that line the surface of tissues and structures throughout the body, particularly affecting systems affiliated with mucosa, which includes the respiratory, digestive, urinary, reproductive and immune systems. The disorder is attributed to improper formation of desmosomes and gap junctions, which prevents proper cornification of the epithelial layer of the skin. Pathophysiology
Desmosomes are extracellular protein structures responsible for cellular adhesion, whereby cells of the same type are held closely together. Gap junctions are specialized channels located within the cell membrane of many animal cell types, which serve as gateways that connect the cytoplasmic interior of two adjacent cells, allowing the passage of small molecules such as ions, nucleotides, second messengers and others. The movement and exchange of small molecules between cells is an important part of intracellular communication processes like cell signaling. Diagnosis
Treatment
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Diagnosis
In acute cases, with a large amount of blood loss, patients may present with anemia or low blood pressure. However, aside from the melena itself, many patients may present with few symptoms. Often, the first approach is to use endoscopy to look for obvious signs of a bleed. In cases where the source of the bleed is unclear, but melena is present, an upper endoscopy is recommended, to try to ascertain the source of the bleed.Lower gastrointestinal bleeding sources usually present with hematochezia or frank blood. A test with poor sensitivity/specificity that may detect the source of bleeding is the tagged red blood cell scan. This is especially used for slow bleeding (<0.5 ml/min). However, for rapid bleeding (>0.5 ml/min), mesenteric angiogram ± embolization is the gold standard. Colonoscopy is often first line, however. Melena versus hematochezia
Bleeds that originate from the lower gastrointestinal tract (such as the sigmoid colon and rectum) are generally associated with the passage of bright red blood, or hematochezia, particularly when brisk. Only blood that originates from a more proximal source (such as the small intestine), or bleeding from a lower source that occurs slowly enough to allow for enzymatic breakdown, is associated with melena. For this reason, melena is often associated with blood in the stomach or duodenum (upper gastrointestinal bleeding), for example by a peptic ulcer.