4.2 Neurological Assessment: Dermatomes, Myotomes & Reflexes

Neurological Assessment: Dermatomes, Myotomes & Reflexes

Clinical Core: Neurological screening is an essential component of orthopedic physical examination whenever a patient reports numbness, paresthesias, radiating pain, uncoordinated motor control, or progressive muscular weakness. By systematically testing the neurological triad—dermatomes (sensory afferents), myotomes (motor efferents), and deep tendon reflexes (monosynaptic arcs)—the Registered Massage Therapist accurately pinpoints spinal nerve root lesions (radiculopathy), isolates peripheral nerve entrapments, and screens for urgent central nervous system pathologies (myelopathy).

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1. Principles of Neurological Screening in Manual Therapy

A targeted neurological screening examination answers three fundamental clinical questions:

1. Is the patient's symptom complex driven by nervous system involvement? (Distinguishing neurogenic symptoms from mechanical myofascial pain, joint dysfunction, or visceral referral).
2. What is the anatomical level and structural locus of the lesion? (Differentiating a single spinal nerve root radiculopathy from an isolated peripheral nerve entrapment or multi-level polyneuropathy).
3. Is the pathology located within the Central Nervous System (Upper Motor Neuron) or Peripheral Nervous System (Lower Motor Neuron)? (Identifying red flag conditions like spinal cord compression or cauda equina syndrome requiring emergency medical referral).

The Neurological Triad Framework

• Dermatome Testing: Evaluates cutaneous sensory afferent pathways entering a single dorsal nerve root.
• Myotome Testing: Evaluates somatic motor efferent pathways arising from a single ventral nerve root to supply a specific group of muscles.
• Reflex Testing (DTR): Evaluates the functional integrity of both the sensory afferent spindle limb, the central spinal cord synapse, and the motor efferent alpha motor neuron limb in a single monosynaptic stretch reflex arc.

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2. Sensory Evaluation: Dermatome Distribution & Examination Protocols

A dermatome is a circumscribed area of cutaneous skin whose sensory receptors and afferent nerve fibers project into the dorsal root of a single specific spinal nerve. Because significant overlapping innervation exists between adjacent cutaneous nerve roots (especially for tactile light touch), pure sensory deficits are most pronounced at the autonomous sensory focal point of each dermatome.

Complete Dermatomal Mapping: C2 through S2

Clinical Examination Protocols for Sensory Pathways

To conduct an accurate sensory evaluation, the clinician tests at least two distinct neurosensory pathways:

1. Tactile Light Touch (Dorsal Column-Medial Lemiscal Pathway):
   • Tool: A light wisp of cotton wool, a soft camel-hair brush, or delicate feather-light fingertip touch.
   • Method: Instruct the patient to close their eyes. Lightly touch the autonomous sensory landmark of each dermatome. Ask the patient: "Say 'yes' the moment you feel the touch, and tell me if it feels identical on both sides."
2. Sharp/Dull Discrimination (Spinothalamic Pathway):
   • Tool: A sterile, single-use neurological pin, broken cotton-tipped wooden applicator, or dedicated sensory wheel (never use unsterilized reusable needles).
   • Method: With the patient's eyes closed, alternate between the sharp point and dull head of the instrument in an unpredictable, random sequence. Ask: "Is this sharp or dull?" followed by: "Does the sharpness feel identical, sharper, or duller compared to the opposite, unaffected side?"
3. Thermal Discrimination (Spinothalamic Pathway):
   • Utilized if sharp/dull testing is equivocal. Contact the skin using two glass tubes or metal thermal rollers filled with warm water (40°C) and cool water (20°C).

Clinical Sensory Terminology

• Anesthesia: Complete absence of all cutaneous sensory perception.
• Hypoesthesia: Reduced or diminished tactile or thermal sensitivity.
• Hyperesthesia: Abnormally heightened cutaneous sensitivity to sensory stimuli.
• Paresthesia: Spontaneous abnormal sensations, such as "pins and needles," burning, or tingling, occurring in the absence of an external stimulus.
• Dysesthesia: An unpleasant, painful abnormal sensation produced by ordinary stimuli.
• Allodynia: Pain triggered by an innocuous stimulus that does not normally provoke pain (e.g., light touch of clothing or a cotton ball eliciting sharp, burning discomfort).

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3. Motor Evaluation: Upper & Lower Quarter Myotomes

A myotome is defined as the collection of skeletal muscle fibers innervated by motor axons emerging from a single spinal nerve root. Because almost every peripheral skeletal muscle receives multi-level innervation from two or more adjacent spinal cord segments, complete flaccid paralysis of a muscle rarely results from a single nerve root compression. Instead, radicular pathology presents as measurable weakness and rapid fatigability in the muscles primarily supplied by that root.

Upper Quarter Myotome Screening Protocol (C1–T1)

During upper quarter screening, the patient sits upright on the treatment table. The clinician applies firm, gradually progressive isometric resistance held steadily for 5 full seconds to detect neurological motor fade:

• C1 & C2 — Cervical Flexion: Patient tucks chin and flexes cervical spine; therapist applies isometric extension resistance against the forehead. (Primary muscles: rectus capitis anterior, longus capitis).
• C3 — Cervical Lateral Flexion: Patient laterally flexes neck toward one shoulder; therapist applies resistance against the temporal-parietal region. (Primary muscles: scalenus anterior/medius, levator scapulae, splenius cervicis).
• C4 — Shoulder Girdle Elevation (Shrug): Patient elevates both shoulder girdles toward ears; therapist places palms over the superior aspect of the acromion and pushes downward into depression. (Primary muscles: upper trapezius, levator scapulae).
• C5 — Shoulder Abduction: Patient abducts arms to 80°–90° in the coronal plane with elbows flexed at 90°; therapist applies downward force at distal humerus. (Primary muscles: middle deltoid, supraspinatus).
• C6 — Elbow Flexion & Wrist Extension:
  • Elbow Flexion: Elbow flexed at 90°, forearm supinated; therapist applies extension force at distal forearm. (Primary muscles: biceps brachii, brachialis).
  • Wrist Extension: Wrist extended with fingers relaxed; therapist applies flexion force to the dorsum of the metacarpals. (Primary muscles: extensor carpi radialis longus/brevis, extensor carpi ulnaris).
• C7 — Elbow Extension & Wrist Flexion:
  • Elbow Extension: Arm abducted, elbow held in partial flexion; therapist pushes elbow toward flexion while stabilizing shoulder. (Primary muscle: triceps brachii).
  • Wrist Flexion: Wrist flexed; therapist applies extension force across palmar metacarpals. (Primary muscles: flexor carpi radialis, flexor carpi ulnaris).
• C8 — Thumb Extension & Finger Flexion:
  • Thumb Extension: Patient points thumb upward toward ceiling in plane of palm; therapist pushes thumb downward into flexion. (Primary muscles: extensor pollicis longus and brevis).
  • Finger Flexion: Patient curls distal phalanges into a tight hook; therapist attempts to pull distal phalanges into extension. (Primary muscle: flexor digitorum profundus).
• T1 — Finger Abduction & Adduction: Patient spreads all fingers widely apart; therapist attempts to squeeze fingers together across the second and fifth digits. (Primary muscles: dorsal interossei [abduct] and palmar interossei [adduct]).

Lower Quarter Myotome Screening Protocol (L1–S2)

Lower quarter testing is typically performed with the patient seated or supine on the examination table:

• L1 & L2 — Hip Flexion: Seated; patient actively lifts knee toward chest; therapist places hands over distal anterior thigh and pushes downward toward floor. (Primary muscles: psoas major, iliacus, pectineus).
• L3 — Knee Extension: Seated with knees flexed over table edge; patient extends knee to approximately 30° of flexion; therapist applies posterior force against the anterior distal tibia. (Primary muscle: quadriceps femoris).
• L4 — Ankle Dorsiflexion: Seated or supine; patient actively dorsiflexes ankle and slightly inverts; therapist applies downward plantarflexion force against the dorsal medial foot. (Primary muscle: tibialis anterior).
• L5 — Great Toe Extension: Seated or supine; patient points great toe toward ceiling; therapist applies downward flexion resistance against the dorsal distal phalanx of the hallux. (Primary muscle: extensor hallucis longus).
• S1 — Ankle Plantarflexion & Eversion:
  • Plantarflexion: Standing; patient performs 10–20 single-leg heel raises on the symptomatic limb. (True neurological S1 weakness prevents sustained unilateral heel raising). In non-weight-bearing supine: patient pushes downward like stepping on a gas pedal against firm resistance. (Primary muscles: gastrocnemius, soleus).
  • Eversion: Patient everts foot outward; therapist applies inversion force against lateral border of 5th metatarsal. (Primary muscles: fibularis longus and brevis).
• S2 — Knee Flexion: Prone; patient flexes knee to 45°–60°; therapist attempts to pull leg into full extension by grasping the posterior distal tibia. (Primary muscles: hamstrings — biceps femoris, semitendinosus, semimembranosus).

Break Test vs. Pain Inhibition

During isometric myotomal testing, the therapist must distinguish true neurological weakness from pain-inhibited weakness:

• Neurological Root Weakness: The muscle resists initially, then exhibits a smooth, involuntary, progressive "fatigue giveaway" as continuous motor unit recruitment collapses under sustained isometric load, usually without sharp local pain.
• Pain-Inhibited Weakness: The contraction breaks suddenly and erratically, accompanied by facial wincing, guarding, and immediate subjective complaint of acute local joint or tendon pain at the site of mechanical irritation.

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4. Deep Tendon Reflexes (DTR) & Reflex Arc Neurophysiology

Deep Tendon Reflexes (more accurately termed myotatic stretch reflexes) evaluate the intactness of an involuntary, monosynaptic reflex circuit operating at a specific segment of the spinal cord.

MONOSYNAPTIC REFLEX CIRCUIT:

[Reflex Hammer Strike] ──> Rapid Muscle Stretch
                               │
                               ▼
                    [Muscle Spindle (Ia Afferent)]
                               │
                               ▼ (Enters Dorsal Horn via Dorsal Root)
                     [Spinal Cord Grey Matter]
                               │
                               ▼ (Monosynaptic Excitatory Synapse)
                    [Alpha Motor Neuron in Ventral Horn]
                               │
                               ▼ (Exits Ventral Root to Efferent Axon)
                    [Rapid Muscle Contraction / Twitch]

Clinical Reflex Examination Methodology

1. Patient Positioning: The target limb must be fully relaxed and supported in a mid-range, neutral resting position. Any active muscular contraction or guarding dampens or distorts the reflex arc.
2. Tendon Location: Palpate the tendon directly. For the biceps reflex, place the examiner's thumb firmly over the biceps tendon in the cubital fossa and strike your own thumb.
3. Hammer Action: Deliver a crisp, brisk tap by flicking the wrist loosely, allowing the weighted head of the reflex hammer to bounce cleanly off the tendon.
4. Bilateral Comparison: Always test the unaffected contralateral limb immediately after to compare reflex amplitude and velocity.

Essential Reflex Testing Levels

The 0 to 4+ Reflex Grading Scale

Reflex responses are commonly documented on the standard 0 to 4+ grading scale (the NINDS-style scale; the separate Wexler scale runs 0 to 5):

• 0 — Absent: No visible or palpable muscle contraction; completely absent reflex even with reinforcement.
• 1+ — Hypoactive / Diminished: Sluggish or trace response; barely palpable contraction with minimal joint movement; often requires reinforcement.
• 2+ — Normal: Average, brisk reflex response; visible muscle twitch with appropriate, controlled joint excursion.
• 3+ — Hyperactive / Brisk: Exaggerated, brisk response; excessive joint excursion; may indicate upper motor neuron disinhibition or systemic anxiety, but not necessarily pathological unless asymmetric.
• 4+ — Markedly Hyperactive with Clonus: Very brisk, hyperactive response accompanied by transient or sustained clonus (rhythmic muscular contractions); unequivocally pathological, indicating Upper Motor Neuron disease.

Reflex Reinforcement: The Jendrassik Maneuver

If a peripheral reflex appears sluggish or absent (0 or 1+), the clinician performs a reinforcement maneuver to facilitate the reflex arc before documenting an absent response:

• For Lower Extremity Reflexes (Patellar/Achilles): The patient interlocks the flexed fingers of both hands across their chest and pulls forcefully outward against resistance without separating them (the Jendrassik maneuver) immediately prior to the hammer strike.
• For Upper Extremity Reflexes: The patient is instructed to clench their jaw or squeeze their knees tightly together.
• Neurophysiological Mechanism: Reinforcement produces general central nervous system motor facilitation, increasing gamma motor neuron discharge to the intrafusal muscle spindle fibers and reducing supraspinal presynaptic inhibition at the spinal segment, thereby enhancing reflex sensitivity.

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5. Upper Motor Neuron (UMN) vs. Lower Motor Neuron (LMN) Lesions

Differentiating between an Upper Motor Neuron lesion and a Lower Motor Neuron lesion is the most critical diagnostic triage task performed during a neurological screening examination.

Anatomical Definitions

• Upper Motor Neurons (UMN): Motor neurons whose cell bodies reside in the cerebral motor cortex or brainstem, whose axons descend via the corticospinal (pyramidal) and corticobulbar tracts through the internal capsule, brainstem, and spinal cord to synapse on lower motor neurons. Lesions involve the brain or spinal cord (e.g., ischemic stroke, traumatic brain injury, multiple sclerosis, cervical spondylotic myelopathy, thoracic cord compression).
• Lower Motor Neurons (LMN): Motor neurons whose cell bodies reside in the anterior (ventral) grey horns of the spinal cord or motor cranial nerve nuclei, whose axons emerge through the ventral roots to form peripheral nerves that terminate directly at neuromuscular junctions in skeletal muscle. Lesions involve the anterior horn cells, spinal nerve roots, nerve plexuses, or peripheral nerves (e.g., disc herniation radiculopathy, thoracic outlet syndrome, carpal tunnel syndrome, Bell's palsy, peripheral neuropathy).

Comprehensive Comparison Table: UMN vs. LMN Findings

Pathological Reflex Testing Procedures

1. Babinski Sign (Plantar Response):
   • Procedure: Firmly stroke the lateral aspect of the plantar surface of the foot with a blunt object (such as the tip of the reflex hammer handle), curving medially across the metatarsal heads toward the base of the great toe.
   • Normal (Negative) Adult Response: Plantarflexion of all toes (flexor response).
   • Pathological (Positive) UMN Response: Dorsiflexion (extension) of the great toe accompanied by fanning (abduction) of the remaining toes. This confirms corticospinal tract disinhibition.
2. Hoffmann's Sign:
   • Procedure: Support the patient's relaxed hand. Grasp the distal interphalangeal (DIP) joint of the middle finger between your index finger and thumb, and briskly flick the patient's fingernail downward.
   • Normal Response: No involuntary movement of the adjacent digits.
   • Pathological (Positive) UMN Response: Sudden, involuntary flexion and adduction of the thumb and index finger. Indicates cervical spinal cord compression (cervical myelopathy).
3. Clonus Test:
   • Procedure: Support the patient's lower leg in slight knee flexion. Rapidly and forcefully dorsiflex the patient's foot, maintaining firm pressure against the sole.
   • Normal Response: No oscillatory beats, or 1–2 unsustained beats that extinguish immediately.
   • Pathological (Positive) UMN Response: Sustained, rhythmic, involuntary oscillations (>3–4 beats or continuous) driven by repetitive spinal stretch reflex activation lacking cortical inhibition.

Clinical Red Flag Triage: When to Refer Immediately

If a neurological screening reveals any of the following Upper Motor Neuron or severe neurological signs, manual therapy must be discontinued immediately, and urgent medical evaluation initiated:

• Positive Babinski sign or positive Hoffmann's sign, especially when accompanied by clumsy, uncoordinated hands or gait ataxia (cervical myelopathy).
• Sustained ankle clonus (≥4 beats).
• Progressive bilateral lower extremity weakness or hyperreflexia.
• Saddle anesthesia accompanied by acute bowel or bladder dysfunction (Cauda Equina Syndrome — surgical emergency).
• Rapidly progressive motor weakness across multiple myotomes over hours or days.