What are the pathophysiological mechanisms and types of central nervous system tuberculosis?

Central Nervous System Tuberculosis: Pathophysiological Mechanisms and Types

CNS tuberculosis develops through hematogenous dissemination of Mycobacterium tuberculosis to the brain and meninges during initial infection, forming tuberculomas that can rupture into cerebrospinal fluid, triggering meningitis, or remain localized as mass lesions, with pathophysiology involving direct bacterial invasion, immune-mediated injury, vasculitis, and infarction. 1, 2

Primary Pathophysiological Mechanisms

Hematogenous Dissemination and Initial Seeding

• M. tuberculosis reaches the CNS through bloodstream dissemination during primary infection or reactivation, depositing bacilli in the brain parenchyma and meninges 2
• Foreign antigens deposited in brain parenchyma are not detected efficiently by the immune system, allowing bacterial survival and tuberculoma formation 2
• Miliary pulmonary tuberculosis is frequently linked to CNS tuberculosis and indicates worse prognosis 3

Tuberculoma Formation and Rupture

• Tuberculomas form around M. tuberculosis deposits in the brain parenchyma and meninges during initial hematogenous dissemination 2
• Tuberculous meningitis develops when these tuberculomas rupture into the cerebrospinal fluid 2
• Paradoxical enlargement or new development of intracranial tuberculomas can occur weeks to months after starting anti-tuberculous therapy due to delayed immune recognition 2

Immune-Mediated Mechanisms

• Direct bacterial invasion causes neuronal and glial cell damage 1, 4
• Immune-mediated injury occurs through autoantibodies against nervous tissue autoantigens 5
• Recent evidence demonstrates that Mtb infection induces ferroptosis in microglia through the Sp1-Mettl14-Acsl4 axis, characterized by ferrous ion accumulation, lipid ROS increase, and glutathione depletion 6

Vascular Complications

• Vasculitis of basal perforating arteries leads to cerebral infarction, particularly affecting the basal ganglia and internal capsule 1, 4
• Ischemic alterations result from immune-complex-mediated vasculitis 5
• Strokes and transient ischemic attacks severely affect prognosis and quality of life 3

Clinical Types and Manifestations

Tuberculous Meningitis (Most Common Form)

• Presents with subacute to chronic course featuring fever, headache, altered mental status, and cranial nerve palsies 1, 4
• CSF findings include lymphocytic pleocytosis, markedly elevated protein (often >100 mg/dL), and low glucose (<45 mg/dL) 1
• Represents 69.9% of CNS tuberculosis cases in endemic regions 7
• Complications include hydrocephalus (requiring CSF diversion), cranial nerve palsy, and basal arteritis with infarction 5, 4, 8

Intracranial Tuberculomas

• Present as localized mass lesions causing focal neurological deficits, seizures, or increased intracranial pressure 4, 8
• Can mimic brain tumors or other infectious processes on imaging 9
• May develop or enlarge paradoxically during treatment due to immune reconstitution 2

Tuberculous Abscess

• Rare manifestation that can mimic pyogenic abscess, requiring high index of suspicion 8
• Distinguished from tuberculomas by liquefactive necrosis and more acute presentation 4

Spinal Tuberculosis

• Includes Pott's spine (vertebral tuberculosis), tuberculous arachnoiditis, and intramedullary tuberculomas 7, 8
• Presents with gradual onset paraplegia, transverse myelitis, or radiculopathy 5, 1
• MRI shows spinal cord enlargement with contrast enhancement in acute phase 5, 10
• 75.56% of Pott's spine patients improve with anti-tuberculosis treatment alone 7

Tuberculous Pachymeningitis and Arachnoiditis

• Rare in children but can cause severe complications 8
• Optochiasmatic arachnoiditis severely affects prognosis and quality of life 3

Special Pathophysiological Considerations

Disseminated Tuberculosis

• 20.26% of CNS tuberculosis cases occur as part of disseminated disease 7
• Associated with significantly poorer outcomes and higher culture positivity rates 7
• Requires evaluation for concurrent neurologic complications even with indolent CNS symptoms 5

Drug-Resistant Tuberculosis

• 27.02% of culture-positive tuberculous meningitis cases in endemic areas show multidrug-resistant tuberculosis 7
• Drug-resistant tuberculous meningitis poses significant diagnostic and treatment challenges with high mortality risk 3

HIV Coinfection

• Complicates diagnosis and treatment, increasing risk of CNS tuberculosis 4
• TB-associated immune reconstitution inflammatory syndrome (IRIS) can occur after antiretroviral therapy initiation 4
• HIV prevalence is an important moderator of CNS tuberculosis prevalence 11

Key Pathophysiological Pitfalls

Do not assume negative serology excludes CNS tuberculosis—serology is negative in more than 50% of neuroschistosomiasis cases and may take up to 22 weeks to become positive in tuberculosis 10

Recognize that CSF eosinophilia occurs in less than 50% of neuroschistosomiasis cases and occasionally in tuberculosis, making it an unreliable diagnostic marker 5, 10

Nearly half of tuberculous meningitis patients exhibit impaired cognition, emphasizing the need for early diagnosis and treatment to prevent permanent neurological sequelae 3

The global mortality of tuberculous meningitis reaches 42.12% in hospitalized patients, with highest prevalence in developing countries with low Human Development Index 11