Hippocampal syndrome secondary to tuberculosis: From neuroinflammation to neurodegeneration

Abstract

Background: Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a primary global health concern, with significant long-term sequelae. Central nervous system TB (CNS-TB) is a clinical spectrum with entities such as tuberculous meningitis and tuberculomas. Emerging evidence suggests that Mtb may directly or indirectly affect the hippocampus, a critical memory, learning, and cognition structure.

Objectives: This review aims to summarize the current biological understanding of Mtb's impact on the hippocampus, elucidate its potential role in neurodegeneration, and introduce the concept of "Hippocampal syndrome secondary to tuberculosis (HSST)" as a novel chronic entity within the CNS-TB spectrum.

Methods: A comprehensive literature review was conducted to analyze how Mtb gains access to the brain, its neurotropism, and the resulting neuroinflammatory and neurodegenerative effects on the hippocampus. Data from clinical, histopathological, and experimental studies were evaluated to assess potential links between TB and cognitive impairment.

Results: Mtb can access the CNS through hematogenous dissemination, the "Trojan Horse" mechanism, or via the olfactory pathway, bypassing the blood-brain barrier (BBB). Once in the brain, Mtb induces chronic neuroinflammation and disrupts hippocampal structure. Studies suggest that TB increases the risk of Alzheimer's and Parkinson's diseases, with evidence of Mtb-driven amyloid-beta accumulation and neuronal loss. Furthermore, specific Mtb strains exhibit neurotropism and produce virulence factors that facilitate CNS invasion.

Conclusions: Understanding the interaction between TB and neurocognitive disorders is critical for improving post-TB care. Recognizing HSST as a chronic condition within the CNS-TB spectrum may support early diagnosis and targeted interventions to mitigate long-term neurological consequences.

Keywords: Alzheimer's disease; CNS-TB; Cognitive impairment; Dementia; Hippocampus; Neurodegeneration; Neuroinflammation; Tuberculosis.