As defined in the Project Management Body of Knowledge (PMBOKv5):
A Project Management Information System (PMIS) is an information system consisting of the tools and techniques used to gather, integrate, and disseminate the outputs of project management processes. It is used to support all aspects of the project from initiating through closing, and can include both manual and automated systems.
PMIS is part of Enterprise Environment Factors, which are tools, for example project management tools like MS-Project or any other automated tool which can make the Project Management activities easier for the project manager. For example in some organizations, every project needs to use their internal Defect management system, which is another example for a PMIS.
Information Management Systems, on the other hand, as defined per the PMBOKv5:
Are facilities, processes, and procedures used to collect, store, and distribute information between producers and consumers of information in physical or electronic format.
More details regarding Information Management Systems as defined in the PMBOKv5 (p. 306):
An information management system provides a set of standard tools for the project manager to capture, store, and distribute information to stakeholders about the project’s costs, schedule progress, and performance. Some software packages allow the project manager to consolidate reports from several systems and facilitate report distribution to the project stakeholders. Examples of distribution formats may include table reporting, spreadsheet analysis, and presentations. Graphic capabilities can be used to create visual representations of project performance
information.
In summary, Information Management Systems are related to ‘Communication Methods’ and tools that the project manager will use in Project Communications Management.