OVERVIEW
Colorectal melanosis (MC) is a mucosal pigmented lesion in which macrophages within the lamina propria of the colorectum contain lipofuscin-like material. With the improvement of people’s living standards, the incidence of colorectal melanosis has increased. The disease is less reported in China. The etiology and pathogenesis of colorectal melioidosis are still unclear, patients with this disease may have electrolyte disorders, and the incidence of colorectal cancer and colorectal adenomatous polyps is high in patients with this disease, and a small number of patients may have pseudostenosis, which may result in caesarean section surgery by mistake.
Etiology
The etiology of colorectal and rectal melanosis is still unclear, but its incidence has increased in recent years, may be related to the improvement of living standards, fat, protein intake increases, fiber intake decreases, constipation patients, as well as anterior protrusion of the rectum, rectal intussusception, slowing down of the colon transport function leading to defecation difficulties, and a large number of abusive laxatives. In particular, anthracene-based laxatives are the main cause of melioidosis.
Symptoms
Most patients with colonic and rectal melioidosis have abdominal distension, constipation and difficulty in passing feces, and a few patients have vague abdominal pain and poor appetite. Previously, melanosis invades the nerve plexus of the intestinal wall, causing degenerative changes in the intramucosal nerve plexus, and is thought to be related to electrolyte disorders.
Examination
1. Blood test
Generally normal. A few patients mainly have low sodium, low potassium and low calcium.
2. Endoscopy
There are different degrees of hyperpigmentation in the mucosa of the large intestine. According to the depth of hyperpigmentation, it is divided into Ⅲ degree: ①Ⅰ degree, light dark brown, similar to leopard skin, asymmetric milky-white spots can be seen on the lymphoid follicles, and the vascular texture of the mucosa can be seen vaguely. The lesions mostly invade the rectum or cecum, or in a section of the intestinal mucosa of the colon, the scope of the affected section of the colon is relatively small, and the demarcation line between the hyperpigmented intestinal mucosa and the non-pigmented intestinal mucosa is not forbidden. ② II degree dark brown, dark brown mucosa in the dark brown mucosa between the lines of milky white mucosa, mostly in the left half of the colon or a section of the colon mucosa, mucosal blood vessels are not easy to see. The demarcation line between pigmented and non-pigmented intestinal mucosa is relatively clear. ③ Ⅲ degree, dark brown, in the dark brown mucosa between the small creamy white lines or spots mucosa, mucosal vascular texture can not be seen, this manifestation is mostly seen in the whole colon type. The lesion does not invade the mucosa of the ileum, and the mucosa of the ileocecal valve is mostly uninvolved. The skin of the anal canal below the rectal dentate line is not hyperpigmented. It is generally accepted that hyperpigmentation of the colorectal mucosa in colorectal melioidosis is more common in the cecum.
Diagnosis
The diagnosis can be determined mainly on the basis of the history and endoscopic examination, which shows that the intestinal mucosa has different degrees of hyperpigmentation, as well as endoscopic biopsy of the diseased mucosa for pathological examination, which shows that there are a large number of densely or sparsely distributed macrophages with pigmented particles in their cytoplasm in the lamina propria of the mucosa.
Differential diagnosis
1. Steatorrhea
This disease should be differentiated from “brown bowel syndrome” in patients with steatorrhea, which is a pigmentation around the nuclei of intestinal smooth muscle cells in patients with steatorrhea, which is brown in color, and there is no pigmentation in the lamina propria of the intestinal mucosa.
2. Congestive colitis and intestinal submucosal flaky hemorrhage
Colorectal melanosis patients should also be identified with congestive colitis and intestinal submucosal flaky hemorrhage, the latter two lesions are more limited, and the lesion mucosa is purplish red.
Complications
1. Intestinal obstruction.
2. Dyspepsia
3. Electrolyte metabolic disorders.
Treatment
It has been reported that patients with colorectal and rectal melanosis caused by long-term laxative use for anterior rectal protrusion and internal rectal trochlea have normal bowel movements after anterior rectal protrusion repair and internal trochlea fixation, and the melanosis disappeared after 1 year of laxative use. However, the treatment of patients with colorectal melioidosis without laxatives must be further explored in the light of medical history, dietary habits, lifestyle and other characteristics.