SD was first described by Arnold Pick in 1904 and in modern times was characterized by Professor Elizabeth Warrington in 1975, but it was not given the name semantic dementia until 1989. The clinical and neuropsychological features, and their association with temporal lobe atrophy were described by Professor John Hodges and colleagues in 1992. Presentation
The defining characteristic of SD is decreased performance on tasks that require semantic memory. This includes difficulty with naming pictures and objects, single word comprehension, categorizing, and knowing uses and features of objects. SD patients also have difficulty with spontaneous speech creation, using words such as "this" or "things" where more specific and meaningful words can be used. Syntax is spared, and SD patients have the ability to discern syntactic violations and comprehend sentences with minimal lexical demands. SD patients have selectively worse concrete word knowledge and association, but retain knowledge and understanding of abstract words. SD patients are able to retain knowledge of numbers and music, but have more difficulty with concrete concepts with visual associations. Impairments of processing of phonemic structure and prosodic predictability have also been observed. Genetics
The majority of SD patients have ubiquitin-positive, TDP-43 positive, tau-negative inclusions, although other pathologies have been described more infrequently, namely tau-positive Picks disease and Alzheimers pathology. Of all the FTLD syndromes, SD is least likely to run in families and is usually sporadic. Alzheimers Disease and Semantic Dementia
Alzheimers disease is related to semantic dementia, which both have similar symptoms.
Additional implicated genes include: SMAD4, BMPR1A, PTEN, GREM1, and MUTYH. The only validated genetic cause of SPS is RNF43. However, most individuals with SPS do not have a germline mutation in any of the associated genes, including RNF43. As the underlying genetic risks for SPS are not fully understood, genetic testing is not recommended. Both autosomal dominant and autosomal recessive patterns of inheritance have been reported, as well as sporadic. Individuals with SPS have serrated polyps, which include hyperplastic polyps, traditional serrated adenomas, and sessile serrated polyps. In addition to serrated polyps, adenomas are often identified. Diagnosis
The diagnosis of serrated polyposis syndrome is achieved when either one of two criteria are met: ≥5 serrated lesions/polyps proximal to the rectum (all ≥ 5 mm in size, with two lesions ≥10 mm), or >20 serrated lesions/polyps of any size distributed throughout the large bowel with 5 proximal to the rectum. Any serrated polyp is counted towards the diagnosis, including sessile serrated lesions, hyperplastic polyps, and traditional serrated adenomas. In addition, the cumulative number of serrated lesions is cumulative over time and includes multiple colonoscopies. The diagnosis of SPS is often overlooked, and requires lifelong tracking of cumulative serrated polyps. Treatment
Colonoscopy is the mainstay of treatment for SPS, which allows for the identification of polyps and removal. Polyp removal is recommended to prevent the development of colorectal cancer. If polyps are relatively few, then removal may be achieved with colonoscopy. After polyps are removed, repeat colonoscopy is recommended in 1 to 3 year intervals.