Neurogenic Disorders: A Lesion-Level Framework for Clinical Localization

1.

NEUROLOGY · CIRCUITS
Neurogenic
disorders
share one
endpoint
failing neural circuits
A lesion-level framework for clinical localization

2.

Start with the lesion:
neuron, pathway, or
network
Degenerative
disease
Progressive neuronal loss and protein
or organelle stress.
Movement
disorder
Disrupted motor circuits, often involving
basal ganglia or cerebellar pathways.
Sensitivity
disorder
Impaired sensory receptors, peripheral
nerves, spinal tracts, or central
processing.

3.

WHY DISEASE STARTS
Etiology is usually multifactorial, not a
single trigger
Different exposures can converge on the same cellular pressures.
Genetic
Environmental
Inherited variants can
alter protein handling,
axonal transport, or
excitability.
Age, toxins, vascular
injury, infection, and
metabolic stress can
modify risk.
Shared cellular
pressures
Oxidative stress,
inflammation,
mitochondrial
dysfunction, and
impaired proteostasis
recur across disorders.

4.

A RECURRING PATHOGENIC ARC
Pathogenesis follows a
common cascade
01
Cellular stress accumulates
02 Synapses and axons lose function
03 Neural circuits become less adaptable
04 Selective neuronal populations die
05 Symptoms spread as network reserve falls

5.

COGNITIVE NETWORKS
Alzheimer disease begins as a
cognitive-network disorder
Progressive cognitive deterioration is the clinical core
Memory networks are affected early, followed by
language, visuospatial, and executive systems
Beta-amyloid deposits and neurofibrillary tangles
characterize the disease
Most cases are sporadic and late-onset; the precise
cause remains unclear

6.

NAME THE LEVEL CORRECTLY
Dementia is a syndrome; Alzheimer
disease is one cause
Dementia
Alzheimer disease
Acquired decline in cognition that
interferes with daily function.
The most common cause of dementia in
older adults, accounting for roughly 60–80%
of cases.
A clinical syndrome with multiple possible
causes.
One disease pattern within the syndrome.
Other degenerative patterns include Lewy body, frontotemporal, and Parkinson-related dementias.

7.

SELECTIVE MOTOR VULNERABILITY
ALS selectively destroys the motor
system
Pathogenic themes include excitotoxicity, impaired RNA or protein handling, axonal transport failure, and
neuroinflammation. Most cases are sporadic; familial forms and multiple genetic and environmental contributors exist.

8.

LOCALIZE THE OUTPUT
Movement disorders are circuit
disorders with recognizable signatures
Clinical localization also includes cortical, brainstem, and peripheral motor systems.

9.

FOLLOW THE SIGNAL
Sensory disorders reveal where the
signal is interrupted
Peripheral
Spinal
Central
Length-dependent
neuropathy, radiculopathy, or
focal nerve injury
Dorsal-column,
spinothalamic, or dorsalroot involvement
Thalamic, brainstem, or
cortical sensory-network
dysfunction
Symptoms may be negative—loss of sensation—or positive—pain, paresthesia, or allodynia.

10.

Compare disorders by cell type, circuit, and
symptom spread
Disorder
Primary vulnerability
Signature pathology
Dominant clinical pattern
Alzheimer
disease
Cognitive networks
Amyloid deposits and tau
tangles
Progressive cognitive decline
Dementia
syndrome
Multiple possible
networks
Cause-dependent
Loss of cognition and function
ALS
Upper and lower motor
neurons
Motor-neuron
degeneration
Weakness, bulbar and respiratory
involvement
Movement
disorders
Motor circuits
Circuit imbalance or
degeneration
Too little, too much, or poorly
patterned movement
Sensory
disorders
Sensory receptors,
nerves, tracts, or cortex
Signal interruption or
maladaptive processing
Loss, tingling, pain, or altered
sensation