Numbness,Tingling, and Sensory Loss¶

Chapter 27 | Harrison's 22e · Part 2 – Cardinal Manifestations & Presentation · Chapter 27

Key Clinical Points¶

Paresthesias (tingling/pins-and-needles) are positive symptoms; Dysesthesias include all abnormal sensations, including painful ones.
Positive symptoms result from increased excitability or lowered thresholds and do not necessarily indicate sensory loss.
Negative symptoms (numbness) typically require the loss of at least one-half of afferent axons to be clinically detectable.
Spinothalamic pathway (anterolateral system): Small fibers; carries nociception, itch, temperature sensation, and touch.
Posterior column–lemniscal system: Large fibers; carries tactile sense, position sense, and kinesthesia.
Sensory ataxia results from impaired deep sensation (proprioception), leading to imbalance, clumsiness of precision movements, and unsteadiness of gait.
Romberg sign is positive if the patient sways or topples when standing with feet together and eyes closed.
Allodynia: Perception of a non-painful stimulus as painful; Hyperalgesia: Severe pain in response to a mildly noxious stimulus.
Hyperpathia: Broad term for hyperesthesia, allodynia, and hyperalgesia where the threshold is increased/delayed but perception is intense once felt.
Vibration testing utilizes a 128 Hz tuning fork to assess large-fiber pathways.

DEFINITION & CLASSIFICATION¶

• Paresthesias: General term for positive symptoms; typically refers to tingling or "pins-and-needles" sensations. • Dysesthesias: Broad term for all types of abnormal sensations, including painful ones, regardless of whether a stimulus is evident. • Hypoesthesia/Hypesthesia: Reduction of cutaneous sensation to specific stimuli (pressure, light touch, warm/cold). • Anesthesia: Complete absence of skin sensation to the same stimuli plus pinprick. • Hypalgesia/Analgesia: Reduced or absent pain perception (nociception). • Hyperesthesia: Increased sensitivity in response to touch. • Allodynia: A non-painful stimulus, once perceived, is experienced as painful (e.g., vibration from a tuning fork). • Hyperalgesia: Severe pain in response to a mildly noxious stimulus. • Hyperpathia: Broad term encompassing hyperesthesia, allodynia, and hyperalgesia; the threshold for a sensory stimulus is increased and perception is delayed, but once felt, it is intensely painful.

ETIOLOGY & PATHOPHYSIOLOGY¶

• Positive vs. Negative Symptoms: • Positive symptoms: (e.g., tingling, itch, pricking, bandlike, lightning-like, aching, knifelike, twisting, drawing, pulling, tightening, burning, searing, electrical, or raw feelings). • Mechanism: Result from trains of impulses generated at sites of lowered threshold or heightened excitability along a peripheral or central sensory pathway. • Clinical Note: Not necessarily associated with sensory deficit on examination. • Negative symptoms: (e.g., numbness; loss of sensation). • Mechanism: Represent loss of sensory function due to afferent axon loss. • Detection Threshold: At least one-half of the afferent axons innervating a site must be lost or functionless before a deficit is clinically detectable. • Anatomy of Sensation: • Cutaneous Receptors: • Nociceptors: Naked nerve endings responding to tissue-damaging stimuli. • Thermoreceptors: Respond to noninjurious thermal stimuli. • Mechanoreceptors: Encapsulated terminals (several types) activated by physical deformation or stretch. • Spinothalamic Pathway (Anterolateral System): • Fibers: Small fibers (unmyelinated and small myelinated). • Function: Nociception, itch, temperature sensibility, and touch. • Path: Cross and ascend in opposite/lateral columns → Ventral posterolateral (VPL) nucleus of the thalamus → Postcentral gyrus. • Posterior Column–Lemniscal System: • Fibers: Large fibers. • Function: Tactile sense, position sense, and kinesthesia. • Path: Project rostrally in posterior/posterolateral columns (same side) → Gracile or cuneate nucleus of the lower medulla → VPL nucleus of the thalamus → Postcentral gyrus.

CLINICAL FEATURES¶

• Sensory Ataxia: • Cause: Disorders of deep sensation (muscle spindles, tendons, and joints) affecting proprioception. • Symptoms: Imbalance (especially with eyes closed or in the dark), clumsiness of precision movements, and unsteadiness of gait. • Examination Findings: Reduced or absent joint position and vibratory sensation; absent deep tendon reflexes in affected limbs. • Romberg Sign: • Positive finding: Patient sways markedly or topples when standing with feet close together and eyes closed. • Severe Deafferentation: • Symptoms: Inability to walk, stand unaided, or sit unsupported. • Complication: Continuous involuntary movements (pseudoathetosis) of the outstretched hands and fingers, particularly with eyes closed.

DIAGNOSTIC APPROACH¶

Sensory Mapping: Map areas of hypoalgesia or anesthesia by testing radially from a center point.
Pain and Temperature Testing: • Pinprick: Tests cutaneous nociceptors (Small fibers; Spinothalamic pathway). • Warm metal object: Tests cutaneous thermoreceptors for hot (Small fibers; Spinothalamic pathway). • Cold metal object: Tests cutaneous thermoreceptors for cold (Small fibers; Spinothalamic pathway). • Cotton wisp/Fine brush: Tests cutaneous mechanoreceptors and naked endings (Large and small fibers).
Touch Testing: Perform on both hairless and hairy skin to differentiate sensory nerve involvement.
Vibration Testing: • Tool: Tuning fork at 128 Hz. • Clinical Significance: Assesses large-fiber pathways (Posterior column–lemniscal system).
Proprioception/Joint Position: • Method: Passive movement of specific joints to assess integrity of large-fiber pathways.

KEY PEARLS & HIGH-YIELD POINTS¶

• Clinical Correlation (Table 27-1): • Small Fibers: Mediate pain, temperature, and itch; utilize the Spinothalamic (SpTh) pathway. • Large Fibers: Mediate vibration, joint position, and tactile sense; utilize the Posterior Column (Lem) system. • Localization Logic: • Peripheral Nerve Damage: Use Figure 2 to identify specific nerve involvement based on cutaneous fields (e.g., median vs. ulnar). • Spinal Nerve Root Involvement: Use Figure 3 (Dermatomes) to map the level of spinal cord involvement. • Symptom Differentiation: Distinguish between 'positive' symptoms (excitability/threshold issues, not necessarily indicating loss) and 'negative' symptoms (actual loss of function requiring ≥ 50% axon loss for detection).

Reference Tables¶

TABLE 27-1 Testing Primary Sensation SENSE Pain Temperature, heat Temperature, cold Touch Vibration Joint position…¶

Harrison's 22e, p.174

SENSE	TEST DEVICE	ENDINGS ACTIVATED	FIBER SIZE MEDIATING	CENTRAL PATHWAY
Pain	Pinprick	Cutaneous nociceptors	Small	SpTh, also D
	Warm metal object	Cutaneous thermoreceptors for hot	Small
Temperature, cold	Cold metal object	Cutaneous thermoreceptors for cold	Small	SpTh
	Cotton wisp, fine brush	Cutaneous mechanoreceptors, also naked endings	Large and small
Vibration	Tuning fork, 128 Hz	Mechanoreceptors, especially pacinian corpuscles	Large	Lem, also D
	Passive movement of specific joints	Joint capsule and tendon endings, muscle spindles	Large