Language impairments and CNS infections: a review

Introduction: Infectious agents such as viruses, bacteria, parasites, fungi, and arthropods can affect the meninges and/or the brain and trigger/relate to difficulties with language tasks. We reviewed the literature on language impairments in people with Central Nervous System (CNS) infections. Aims: To review published reports of CNS infections that trigger/relate to difficulties with language tasks, to highlight the most commonly infectious agents, and to provide further grounds to study this topic. Methods: PubMed, Medline, Google Scholar, and Web of Science records were examined. Search strings with 70 infection terms and the words aphasia, fluency, language, naming, reading, and writing were used. The reference section and the citations of each study were examined. The type of infection, infectious agent, number of patients, neurological damage, language tests administered, and main findings were noted for each article meeting the inclusion criteria. Results: We found 41 articles published in the last 45 years. Half of the reports were single case (series) and the other half group studies. Infections with 18 agents were detected as triggering/related to difficulties with language tasks. Bacterial meningitis, Herpes Simplex Encephalitis (HSV), and HIV were most commonly reported. Reports of English-speaking patients were most common (46%) followed by other languages spoken in the Western world. Damage to specific cortico-subcortical areas is indicated in half of the studies. Most reports presented cases with diffuse or focal bilateral damage affecting the frontal or temporal lobes. Discussion and conclusion: The current literature is heterogeneous regarding assessment times and language protocols. There is a tendency towards testing language production and administering tests that assess severe language damage. HSV reports use the most in-depth language protocols, probably because of the specific impairments triggered by this disease due to damage to the temporal lobes. Further work may focus on understanding mild language impairments; less explored brain infections, language domains, and modalities (e.g., written/spoken comprehension); risk factors, and impact of co-occurring conditions; and how CNS infections damage the brain (e.g., subcortically). Potential issues such as the presence of delirium, stress/anxiety, and publication biases regarding prevalent infections in the Western world seem relevant to consider.