Sensory System

Dermatomes & Sensory Pathways

From receptor to cortex: dorsal columns vs spinothalamic tract, dermatome landmarks, and the clinical patterns that localize sensory lesions from peripheral nerve to parietal cortex.

Clinical Presets

Lesion Level

Clinical Vignette

A 62-year-old diabetic with burning feet for 2 years, worse at night. Numbness to pinprick up to mid-calf bilaterally. Vibration is reduced at the toes but normal at the ankles. Ankle jerks are absent.

Polyneuropathy (Length-Dependent)

peripheral

Distal peripheral nerves (longest fibers first)

Stocking-glove pattern. Small fibers (pain/temperature) or large fibers (proprioception/vibration) may be preferentially affected.

Sensory Findings

Stocking-glove distribution (distal symmetric)

Distribution: Length-dependent: feet first, then hands as disease progresses

Pain/Temperature

lost

Stocking-glove (distal > proximal)

Longest fibers degenerate first (length-dependent). Small fibers (Aδ, C) carry pain/temperature.

Proprioception/Vibration

diminished

Distal (toes > fingers)

Large fibers are affected later in small fiber neuropathy, or first in large fiber neuropathy.

Light Touch

diminished

Stocking-glove

Variably affected depending on fiber type involvement.

Spared Modalities

  • Proximal sensation (initially)
  • Facial sensation

Key Distinctions

  • Small fiber neuropathy: pain/temperature loss, burning feet, normal NCS
  • Large fiber neuropathy: proprioception/vibration loss, sensory ataxia, abnormal NCS
  • Mixed: both modalities affected — most common

Clinical correlate: Diabetes, alcohol, B12 deficiency, CIDP, amyloidosis

Localization Algorithm

  1. 1.Step 1: Which modalities are affected? (pain/temp vs. proprioception/vibration vs. discriminative)
  2. 2.Step 2: What is the distribution? (nerve, dermatome, stocking-glove, hemibody, suspended/cape, crossed)
  3. 3.Step 3: Are motor signs present? If so, UMN or LMN?
  4. 4.Step 4: Does the sensory pattern match a known tract or syndrome?