Neurosyphilis

Prion diseases: forms and epidemiology

Diseases caused by pathogenic prions have several forms with different transmission routes and age ranges of onset:

• Iatrogenic form. Occurs as a consequence of medical interventions. The main transmission routes are neurosurgical procedures or the use of human growth hormone derived from infected brain tissue. The incubation period lasts from 2 to 20 years.
• New variant form. First recorded in the UK in 1996. It is believed that transmission occurs through the consumption of meat from cattle affected by spongiform encephalopathy ("mad cow disease"). It predominantly manifests in individuals under 50 years of age, with an incubation period also ranging from 2 to 20 years.
• Sporadic form. Most commonly debuts at an older age — from 55 to 70 years.
• Inherited form. Manifests at middle age, typically from 40 to 55 years.

The prognosis for these diseases is extremely poor. In the sporadic form, death occurs within 6 months, and in the inherited form, within 1–2 years after the onset of the first symptoms. There are currently no effective treatments.

Clinical presentation and diagnosis of prion diseases

The symptoms of the disease develop in stages.

Onset of the disease:

• In approximately 33% of patients, the disease begins with memory impairment, behavioral changes, and higher mental function disorders.
• In another 33%, cerebellar ataxia, oculomotor disorders, decreased visual acuity, as well as dizziness and headaches come to the forefront.
• In the remaining third of cases, a mixed picture of the symptoms listed above is observed.

Advanced stage: Characterized by the mandatory presence of mental disorders, which often reach the degree of pronounced dementia. A typical sign is myoclonic hyperkinesia affecting various muscle groups. Visual and oculomotor impairments and ataxia persist and progress.

Diagnosis: Clinical criteria include rapidly progressive dementia in middle-aged and elderly patients, accompanied by ataxia and myoclonus. Instrumental and laboratory confirmations:

• EEG: in the advanced stage, specific triphasic sharp waves (1–2 Hz) or bursts of high-amplitude activity against a flattened background curve are recorded.
• CSF (cerebrospinal fluid): electrophoresis reveals specific changes in the qualitative protein composition.
• MRI: may demonstrate cerebral atrophy, cortical lesions, and basal ganglia involvement.

A definitive (confirmed) diagnosis is established solely by morphology — based on the results of a lifetime brain tissue biopsy or after autopsy.

Patients do not pose a danger during casual contact, so isolation is not required. However, instruments (needles, electrodes) used during the examination of such patients must be strictly destroyed to prevent iatrogenic transmission.

Brain abscess

A brain abscess is a collection of pus that forms as a result of focal inflammation of the brain parenchyma. The formation of an abscess is a prolonged process taking several weeks, starting from localized purulent encephalitis to the formation of a dense capsule.

Etiology and routes of infection: The main cause is the seeding of an infected embolus from other foci. Pathogens are most commonly streptococci and staphylococci. There are two main pathways of spread:

1. Contiguous route (40%): infection spreads from nearby purulent foci (otitis media, mastoiditis, sinusitis).
2. Hematogenous route (33%): infection is bloodborne. This is characteristic of patients with acute infective endocarditis, purulent pulmonary diseases, or congenital heart defects (more often in children).

Less commonly, an abscess becomes a complication of neurosurgical interventions or penetrating traumatic brain injuries.

Clinical presentation: The leading symptom is headache caused by intracranial hypertension. In severe situations, it is accompanied by vomiting, nausea, confusion, and psychiatric abnormalities. At the beginning of the disease, temperature often rises and meningeal signs appear. After 1–2 weeks, the temperature may normalize, indirectly indicating the formation of a capsule around the pus collection. Focal symptoms (ataxia, aphasia, central paresis) gradually increase depending on the location of the lesion. Some patients develop seizure disorders.

The prognosis is serious: mortality ranges from 15 to 25%, and reaches 50% in multiple lesions. Half of the survivors suffer from persistent neurological deficits or symptomatic epilepsy.

Diagnosis and treatment of abscess

Diagnosis is based on medical history, clinical presentation, and neuroimaging data. CT or MRI plays a key role, visualizing lesions as rounded formations with characteristic ring enhancement. A search for the primary source of infection (echocardiography, blood culture, chest and skull radiography/CT) is also mandatory.

Therapeutic approaches:

• Conservative treatment: prolonged (1–2 months) broad-spectrum antibiotic therapy with high doses. Penicillin (up to 300,000 IU/kg/day IV) or a combination of third-generation cephalosporins with metronidazole is used.
• Surgical treatment: indicated in many cases, but performed strictly after the abscess has encapsulated (usually in the 4th–6th week from disease onset).

Subdural empyema and epidural abscess

These two conditions often occur together:

• Subdural empyema — a collection of pus in the space between the arachnoid and dura mater.
• Epidural abscess — a purulent collection between the skull bones and the dura mater.

Infection most commonly enters via contiguous spread from the sinuses (in sinusitis) or ear (in otitis). The hematogenous route and trauma consequences are less common. The main pathogens are streptococci, staphylococci, and Gram-negative flora. Clinically, the diseases manifest with fever, severe headache, meningeal signs, focal neurological deficits, and epileptic seizures.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Morphological changes in brain tissue in prion diseases
• EEG features in various neurodegenerative diseases
• Antibacterial therapy regimens for intracranial infections
• Differential diagnosis of intracranial mass lesions on MRI
• Pathogenesis of brain abscess capsule formation

Other topics in "Chapter 23. Infectious Diseases of the Nervous System"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.