This case was reported in a literature article and described the occurrence of acute disseminated encephalomyelitis in a male subject who received Tdap vaccine. Co-suspect products included meningococcal polysaccharide vaccine groups A, C, W, and Y. On an unknown date, 5 days after receiving Tdap vaccine, the subject developed acute disseminated encephalomyelitis. Serious criteria included GSK medically significant. Additional event included inappropriate age at vaccine administration. The outcome of acute disseminated encephalomyelitis was unknown. The outcome of the additional event included inappropriate age at vaccine administration (unknown). The investigator considered the acute disseminated encephalomyelitis to be possibly related to Tdap vaccine. Additional information was provided. This case was reported in a literature article and described the occurrence of acute disseminated encephalomyelitis (ADEM) in a male patient of unspecified age who was vaccinated with unspecified Tdap vaccine and unspecified meningococcal polysaccharide vaccine (manufacturer unknown for both). The patient was part of the study that aimed to analyse the association of immunisation and subsequent development of transverse myelitis (TM) or ADEM. All cases of TM and ADEM in the Vaccine Safety Datalink (VSD) population were identified. The study used a case-centered design, which compares vaccination patterns during an exposure interval prior to the outcome in cases vs the entire study population, matched by age, sex, and site. Study population included all children and adults of any age enrolled in the health plans at 6 VSD sites who received 1 or more vaccines during the period from 1 January 2007 through 31 December 2012. No information on patient's medical history or family history or concurrent condition or concomitant medication was provided. On an unspecified date, the patient received unspecified Tdap vaccine and unspecified meningococcal polysaccharide vaccine (administration route and site unspecified; dosages unknown; batch number not provided for both). The patient was not recommended for unspecified meningococcal polysaccharide vaccine for his age group at that time. On an unspecified date between 1 January 2007 and 31 December 2012, between 5 and 28 day (risk interval) after vaccination, the patient developed ADEM. (In this study, trained medical records analysts (MRAs) reviewed all identified cases to verify that a neurologist made the diagnosis within 3 months of the first electronic diagnosis, to validate the date of onset, to ensure the diagnosis did not change over time, and to abstract pertinent information. Following this, a neurologist with expertise in demyelinating illnesses reviewed each case. For ADEM, cases were confirmed using the Brighton Collaboration Criteria, and accepted diagnostic levels of certainty 1, 2, and 3 as cases). Treatment was unknown. The outcome of the event was not reported. The authors commented "for ADEM, we found a possible association with the Tdap vaccine in the 5 to 28 day risk interval." The authors concluded "TM and ADEM are rarely, if ever, associated with vaccines. If there is an association of ADEM with Tdap, the excess risk is not likely to exceed 1.16 cases of ADEM per million doses of Tdap administered." This is 1 of the 5 valid cases reported in the same literature article.