Objective We have recently discovered new gastric lesions with black spots. There have been no reports about black spots and their clinicopathological features. We therefore report the clinicopathological features of black spots and assess their causes and mechanisms.

Methods Sixty-four patients with black spots among 26,620 Japanese patients that underwent endoscopy between May 2012 and October 2014 were enrolled. Endoscopic findings of black spots were defined as black pigmentations in the gastric mucosa by conventional endoscopy. We investigated the clinicopathological characteristics, including gender, age, underlying diseases and medications, endoscopic and pathologic findings of patients with black spots.

Results The prevalence of patients with black spots was 0.24%. Of sixty-four cases, 44 (68.8%) were taking proton pump inhibitors (PPIs). Eight (12.5%) were taking corticosteroids. There were 10 cases (15.6%) with decreased renal function. All black spots were identified only in the fundic gland region. Forty-one (64.1%) patients had multiple (more than ten) black spots. There were two different types: black spots on the flat mucosa and black spots on fundic gland polyps. Pathologically, parietal cell protrusions, fundic gland cysts and brownish pigmentation in fundic gland cysts were seen in 26 (76.5%), 23 (67.6%) and 6 (17.6%) patients, respectively.

Conclusion We herein describe gastric black spots as a new gastric mucosal finding that arises only in the fundic gland region. The black spots are pathologically brownish pigmentations in fundic gland cysts. Adverse events of PPIs and parietal cell protrusion caused by PPI use are strongly considered to be one of the etiologies of black spots.