Cervical dermatomes and myotomes US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Cervical dermatomes and myotomes. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Cervical dermatomes and myotomes US Medical PG Question 1: A 16-year-old boy is brought to the emergency department after being tackled at a football game. Per his mom, he is the quarterback of his team and was head-butted in the left shoulder region by the opposing team. Shortly after, the mother noticed that his left arm was hanging by his torso and his hand was “bent backwards and facing the sky.” The patient denies head trauma, loss of consciousness, sensory changes, or gross bleeding. A physical examination demonstrates weakness in abduction, lateral rotation, flexion, and supination of the left arm and tenderness of the left shoulder region with moderate bruising. Radiograph of the left shoulder and arm is unremarkable. Which of the following is most likely damaged in this patient?
- A. C5-C6 nerve roots (Correct Answer)
- B. Ulnar nerve
- C. C8-T1 nerve roots
- D. Long thoracic nerve
Cervical dermatomes and myotomes Explanation: ***C5-C6 nerve roots***
- The "bent backwards and facing the sky" hand posture indicates **Waiter's tip position**, a classic sign of **Erb-Duchenne palsy**, caused by damage to the upper trunk of the brachial plexus (C5-C6 roots).
- Weakness in **abduction** (deltoid, supraspinatus), **lateral rotation** (infraspinatus, teres minor), **flexion** (biceps, coracobrachialis), and **supination** (biceps, supinator) are all consistent with C5-C6 nerve root involvement.
*Ulnar nerve*
- Ulnar nerve damage would result in a **claw hand deformity** (hyperextension of MCP joints and flexion of DIP/PIP joints of 4th and 5th digits) and weakness in intrinsic hand muscles, not the observed upper arm weakness.
- Sensory loss involves the medial hand and little finger.
*C8-T1 nerve roots*
- Damage to the C8-T1 nerve roots (lower trunk) typically results in **Klumpke's palsy**, characterized by a more severe **claw hand** and paralysis of intrinsic hand muscles.
- This presentation does not match the observed functional deficits.
*Long thoracic nerve*
- Injury to the long thoracic nerve causes paralysis of the **serratus anterior muscle**, leading to **scapular winging**, especially when pushing against a wall.
- While possible in shoulder trauma, it does not explain the widespread weakness in abduction, rotation, flexion, and supination of the arm.
Cervical dermatomes and myotomes US Medical PG Question 2: A 53-year-old woman comes to the physician because of a 3-month history of intermittent severe left neck, shoulder, and arm pain and paresthesias of the left hand. The pain radiates to the radial aspect of her left forearm, thumb, and index finger. She first noticed her symptoms after helping a friend set up a canopy tent. There is no family history of serious illness. She appears healthy. Vital signs are within normal limits. When the patient extends and rotates her head to the left and downward pressure is applied, she reports paresthesias along the radial aspect of her left forearm and thumb. There is weakness when extending the left wrist against resistance. The brachioradialis reflex is 1+ on the left and 2+ on the right. The radial pulse is palpable bilaterally. The remainder of the examination shows no abnormalities. Which of the following is the most likely diagnosis?
- A. Carpal tunnel syndrome
- B. Syringomyelia
- C. Amyotrophic lateral sclerosis
- D. C5-C6 disc herniation (Correct Answer)
- E. Thoracic outlet syndrome
Cervical dermatomes and myotomes Explanation: ***C5-C6 disc herniation***
- The patient's symptoms of neck, shoulder, and arm pain, along with paresthesias radiating to the **radial aspect of the forearm, thumb, and index finger**, are consistent with **C6 dermatomal distribution**.
- The positive **Spurling's maneuver** (extension, rotation, and downward pressure causing paresthesias) and decreased **brachioradialis reflex** (C5-C6 reflex) strongly suggest **cervical radiculopathy**, most likely due to a disc herniation affecting the C6 nerve root.
*Carpal tunnel syndrome*
- Characterized by **median nerve compression** at the wrist, causing paresthesias and pain primarily in the **thumb, index, middle, and radial half of the ring finger**, typically worsening at night.
- Would not explain the neck, shoulder, or upper arm pain, or the positive Spurling's maneuver, which indicates a more proximal nerve root compression.
*Syringomyelia*
- A rare chronic progressive disorder where a **syrinx (fluid-filled cyst)** forms within the spinal cord, often presenting with a **cape-like distribution of sensory loss** (loss of pain and temperature sensation) over the shoulders and upper extremities.
- Motor weakness can occur but the pain and paresthesia pattern, along with the positive Spurling's maneuver, are not typical for syringomyelia.
*Amyotrophic lateral sclerosis*
- A progressive neurodegenerative disease affecting **upper and lower motor neurons**, leading to widespread muscle weakness, atrophy, fasciculations, and spasticity.
- It does not typically present with acute, radicular pain and paresthesias restricted to a specific dermatome, and sensory involvement is absent.
*Thoracic outlet syndrome*
- Involves compression of the **brachial plexus** and/or subclavian vessels in the thoracic outlet, causing neurogenic symptoms (pain, paresthesias) primarily in the **ulnar nerve distribution** and vascular symptoms (edema, discoloration).
- The pain and paresthesias in the radial aspect of the hand and forearm, along with the specific reflex changes and positive neck maneuver, are not characteristic of thoracic outlet syndrome.
Cervical dermatomes and myotomes US Medical PG Question 3: A 52-year-old man comes to the physician because of right shoulder pain that began after he repainted his house 1 week ago. Physical examination shows right subacromial tenderness. The pain is reproduced when the patient is asked to abduct the shoulder against resistance with the arm flexed forward by 30° and the thumb pointing downwards. The tendon of which of the following muscles is most likely to be injured in this patient?
- A. Teres minor
- B. Deltoid
- C. Supraspinatus (Correct Answer)
- D. Subscapularis
- E. Infraspinatus
Cervical dermatomes and myotomes Explanation: ***Supraspinatus***
- The patient's presentation with **right shoulder pain** after painting (an overhead activity), subacromial tenderness, and pain reproduced by the described maneuver (the **"empty can" test**) is highly indicative of a **supraspinatus tendon injury**.
- The supraspinatus is the most commonly injured rotator cuff muscle because its tendon passes through the **subacromial space**, making it vulnerable to impaction and degeneration.
*Teres minor*
- The teres minor is primarily involved in **external rotation** and adduction of the shoulder, not typically tested by the "empty can" maneuver.
- Injury to the teres minor is less common than supraspinatus tears and usually presents with weakness in **external rotation**.
*Deltoid*
- The deltoid is a powerful muscle responsible for **shoulder abduction** (especially beyond the initial 15 degrees) and flexion, but it is less commonly involved in isolated tendonitis or tears from repetitive overhead activity.
- Deltoid pain is usually diffuse and does not localize to the **subacromial space** in the same way as supraspinatus pathology.
*Subscapularis*
- The subscapularis is responsible for **internal rotation** and adduction of the shoulder.
- Injuries typically present with weakness in internal rotation and may be tested with specific maneuvers like the **lift-off test** or **belly-press test**.
*Infraspinatus*
- The infraspinatus is a primary **external rotator** of the shoulder.
- While it can be injured in conjunction with the supraspinatus or in isolation, its primary function is external rotation, and specific tests for it involve assessing resistance to **external rotation**.
Cervical dermatomes and myotomes US Medical PG Question 4: A 51-year-old woman comes to the physician because of progressively worsening lower back pain. The pain radiates down the right leg to the lateral side of the foot. She has had no trauma, urinary incontinence, or fever. An MRI of the lumbar spine shows disc degeneration and herniation at the level of L5–S1. Which of the following is the most likely finding on physical examination?
- A. Difficulty walking on heels
- B. Exaggerated patellar tendon reflex
- C. Diminished sensation of the anus and genitalia
- D. Diminished sensation of the anterior lateral thigh
- E. Weak Achilles tendon reflex (Correct Answer)
Cervical dermatomes and myotomes Explanation: ***Weak Achilles tendon reflex***
- A herniated disc at **L5-S1** typically compresses the **S1 nerve root**, which is responsible for the **Achilles tendon reflex**.
- **S1 radiculopathy** presents with weakness in plantarflexion, diminished or absent Achilles reflex, and sensory loss in the **lateral foot** (matching the patient's symptoms).
*Difficulty walking on heels*
- Difficulty walking on heels (**dorsiflexion weakness**) is primarily associated with **L4-L5 disc herniation** compressing the **L5 nerve root**.
- This symptom indicates **L5 radiculopathy**, which affects the tibialis anterior muscle, not S1.
*Exaggerated patellar tendon reflex*
- An exaggerated patellar tendon reflex (**hyperreflexia**) indicates an **upper motor neuron lesion** or spinal cord compression above the lumbar region.
- A disc herniation at **L5-S1** causes a **lower motor neuron lesion** with diminished reflexes, not hyperreflexia.
*Diminished sensation of the anus and genitalia*
- This symptom, along with urinary incontinence and saddle anesthesia, is characteristic of **cauda equina syndrome**, a surgical emergency.
- The patient lacks urinary incontinence and the specific unilateral pain pattern points to isolated **S1 radiculopathy**, not cauda equina syndrome.
*Diminished sensation of the anterior lateral thigh*
- Sensory loss in the **anterior lateral thigh** is associated with compression of the **lateral femoral cutaneous nerve** or **L2-L4 nerve roots**.
- This pattern is not consistent with **L5-S1 disc herniation**, which causes sensory changes in the lateral foot and posterior leg.
Cervical dermatomes and myotomes US Medical PG Question 5: A 40-year-old male presents to the physician's office complaining of an inability to push doors open. He has had this problem since he was playing football with his children and was tackled underneath his right arm on his lateral chest. On examination, he has a winged scapula on the right side. Which of the following nerves is most likely the cause of this presentation?
- A. Phrenic nerve
- B. Spinal accessory nerve
- C. Long thoracic nerve (Correct Answer)
- D. Greater auricular nerve
- E. Musculocutaneous nerve
Cervical dermatomes and myotomes Explanation: ***Long thoracic nerve***
- The **long thoracic nerve** innervates the **serratus anterior muscle**, which is responsible for scapular protraction and upward rotation.
- Damage to this nerve, often from trauma to the lateral chest wall (tackled underneath the arm), leads to paralysis of the serratus anterior and a characteristic **winged scapula** with lateral and inferior prominence.
- Patients have difficulty with **pushing movements** (protraction) and overhead activities.
*Phrenic nerve*
- The **phrenic nerve** primarily innervates the **diaphragm** and is crucial for respiration.
- Damage to the phrenic nerve would cause respiratory compromise, not a winged scapula or difficulty pushing doors.
*Spinal accessory nerve*
- The **spinal accessory nerve (cranial nerve XI)** innervates the **sternocleidomastoid** and **trapezius muscles**.
- Injury to this nerve can cause scapular winging due to **trapezius paralysis**, but the winging is typically **medial** with the inferior angle moving medially, unlike the lateral winging from serratus anterior paralysis.
- The mechanism of injury (lateral chest trauma during tackling) and inability to push are classic for **long thoracic nerve** injury, not spinal accessory nerve.
*Greater auricular nerve*
- The **greater auricular nerve** is a cutaneous nerve that provides sensation to the skin over the parotid gland, mastoid process, and auricle.
- Damage to this nerve would result in sensory loss in these areas and is unrelated to muscle weakness or a winged scapula.
*Musculocutaneous nerve*
- The **musculocutaneous nerve** innervates the **biceps brachii**, **brachialis**, and **coracobrachialis muscles**, responsible for elbow flexion and forearm supination.
- Damage to this nerve would primarily affect these movements and sensation in the lateral forearm, not leading to a winged scapula.
Cervical dermatomes and myotomes US Medical PG Question 6: A 65-year-old female with a past medical history of hypertension presents to her primary care doctor with a 3 month history of spasmodic facial pain. The pain is located in her right cheek and seems to be triggered when she smiles, chews, or brushes her teeth. The pain is sharp and excruciating, lasts for a few seconds, and occurs up to twenty times per day. She denies headaches, blurry vision, facial weakness, or changes in her memory. She feels rather debilitated and has modified much of her daily activities to avoid triggering the spasms. In the clinic, her physical exam is within normal limits. Her primary care doctor prescribes carbamazepine and asks her to follow up in a few weeks. Which cranial nerve is most likely involved in the patient's disease process?
- A. CN III
- B. CN V (Correct Answer)
- C. CN VI
- D. CN VII
- E. CN IV
Cervical dermatomes and myotomes Explanation: ***CN V***
- The patient's presentation of **recurrent, sharp, excruciating, unilateral facial pain** triggered by movements like chewing, smiling, or brushing teeth is classic for **trigeminal neuralgia**.
- **Trigeminal neuralgia** specifically affects the **trigeminal nerve (CN V)**, which has sensory branches covering the face, and is often treated with **carbamazepine**.
*CN III*
- The **oculomotor nerve (CN III)** is primarily involved in **eye movement** and **pupillary constriction**.
- Damage to CN III typically causes **diplopia, ptosis,** and **pupil dilation**, which are not present in this patient's symptoms.
*CN VI*
- The **abducens nerve (CN VI)** controls the **lateral rectus muscle**, responsible for **abducting the eye** (moving it outward).
- Dysfunction typically results in **diplopia** and an inability to move the eye laterally, not facial pain.
*CN VII*
- The **facial nerve (CN VII)** controls **facial expressions**, taste sensation from the anterior two-thirds of the tongue, and lacrimation/salivation.
- While it innervates facial muscles, its involvement typically presents as **facial weakness** or **paralysis** (e.g., Bell's palsy), not sharp, spasmodic pain.
*CN IV*
- The **trochlear nerve (CN IV)** innervates the **superior oblique muscle**, which is involved in rotating and depressing the eye.
- Lesions usually lead to **vertical diplopia**, particularly when looking down and inward, which is unrelated to the described facial pain.
Cervical dermatomes and myotomes US Medical PG Question 7: An 18-year-old man comes to the clinic with his mom for “pins and needles” of both of his arms. He denies any past medical history besides a recent anterior cruciate ligament (ACL) tear that was repaired 1 week ago. The patient reports that the paresthesias are mostly located along the posterior forearms, left more than the right. What physical examination finding would you expect from this patient?
- A. Loss of finger abduction
- B. Loss of forearm flexion and supination
- C. Loss of arm abduction
- D. Loss of thumb opposition
- E. Loss of wrist extension (Correct Answer)
Cervical dermatomes and myotomes Explanation: ***Loss of wrist extension***
- The patient describes "pins and needles" predominantly along the **posterior forearms**, indicating **radial nerve involvement**.
- The **radial nerve** provides sensory innervation to the posterior forearm via the **posterior cutaneous nerve of the forearm**.
- Motor function: The radial nerve innervates the **extensor carpi radialis longus and brevis** and **extensor carpi ulnaris**, which are responsible for **wrist extension**.
- The recent **ACL repair surgery** suggests a **positional compression injury** to the radial nerves from prolonged arm positioning during the procedure.
- Expected finding: **Wrist drop** (inability to extend the wrist against gravity).
*Loss of finger abduction*
- **Finger abduction** is controlled by the **interossei muscles**, which are innervated by the **ulnar nerve**.
- The ulnar nerve provides sensory innervation to the **medial forearm** (via medial cutaneous nerve of forearm) and **medial 1.5 digits**, NOT the posterior forearm.
- Posterior forearm paresthesias do not indicate ulnar nerve involvement.
*Loss of forearm flexion and supination*
- **Forearm flexion** is primarily controlled by the **musculocutaneous nerve** (supplying the **biceps brachii** and **brachialis**).
- The musculocutaneous nerve becomes the **lateral cutaneous nerve of the forearm**, supplying the **lateral forearm**, not the posterior forearm.
- Supination involves the biceps (musculocutaneous) and supinator (radial nerve, posterior interosseous branch).
*Loss of arm abduction*
- **Arm abduction** is primarily controlled by the **deltoid** muscle (innervated by the **axillary nerve**) and **supraspinatus** (suprascapular nerve).
- Axillary nerve injury causes sensory loss over the **lateral shoulder** (regimental badge area), not the forearm.
*Loss of thumb opposition*
- **Thumb opposition** is a function of the **opponens pollicis** and **flexor pollicis brevis** (superficial head), primarily innervated by the **median nerve**.
- Median nerve compression typically causes paresthesias in the **lateral 3.5 digits** and **thenar eminence**, not the posterior forearm.
Cervical dermatomes and myotomes US Medical PG Question 8: A 59-year-old woman presents to the emergency room with severe low back pain. She reports pain radiating down her left leg into her left foot. She also reports intermittent severe lower back spasms. The pain started after lifting multiple heavy boxes at her work as a grocery store clerk. She denies bowel or bladder dysfunction. Her past medical history is notable for osteoporosis and endometrial cancer. She underwent a hysterectomy 20 years earlier. She takes alendronate. Her temperature is 99°F (37.2°C), blood pressure is 135/85 mmHg, pulse is 85/min, and respirations are 22/min. Her BMI is 21 kg/m^2. On exam, she is unable to bend over due to pain. Her movements are slowed to prevent exacerbating her muscle spasms. A straight leg raise elicits severe radiating pain into her left lower extremity. The patient reports that the pain is worst along the posterior thigh and posterolateral leg into the fourth and fifth toes. Palpation along the lumbar vertebral spines demonstrates mild tenderness. Patellar reflexes are 2+ bilaterally. The Achilles reflex is decreased on the left. Which nerve root is most likely affected in this patient?
- A. L5
- B. S2
- C. L3
- D. L4
- E. S1 (Correct Answer)
Cervical dermatomes and myotomes Explanation: ***S1***
- Pain radiating to the **posterior thigh**, **posterolateral leg**, and into the **fourth and fifth toes** is characteristic of **S1 dermatome involvement**.
- A **decreased Achilles reflex** (ankle jerk reflex) specifically points to compromise of the **S1 nerve root**.
*L5*
- **L5 radiculopathy** typically causes pain and sensory deficits in the **dorsum of the foot** and into the **first, second, and third toes**.
- Motor weakness often affects **foot dorsiflexion** and **toe extension**, not primarily the Achilles reflex.
*S2*
- **S2 radiculopathy** would primarily affect sensation along the **posterior thigh** and **calf**, with possible involvement of the **plantar aspect of the foot**.
- It does not typically cause a decrease in the **Achilles reflex**, which is predominantly S1.
*L3*
- **L3 radiculopathy** typically presents with pain and sensory changes along the **anterior thigh** and possibly the **medial knee**.
- It can affect the **patellar reflex**, which is intact in this patient, and does not cause pain in the posterior leg or foot.
*L4*
- **L4 radiculopathy** typically causes pain and sensory changes over the **anterior thigh**, **medial leg**, and potentially the **medial malleolus**.
- It often presents with weakness in **quadriceps muscle** and can cause a diminished **patellar reflex**, which is normal in this patient.
Cervical dermatomes and myotomes US Medical PG Question 9: A 35-year-old woman, gravida 2, para 1, at 40 weeks' gestation, presents to the hospital with contractions spaced 2 minutes apart. Her past medical history is significant for diabetes, which she has controlled with insulin during this pregnancy. Her pregnancy has otherwise been unremarkable. A baby boy is born via a spontaneous vaginal delivery. Physical examination shows he weighs 4.5 kg (9 lb), the pulse is 140/min, the respirations are 40/min, and he has good oxygen saturation on room air. His left arm is pronated and medially rotated. He is unable to move it away from his body. The infant’s right arm functions normally and he is able to move his wrists and all 10 digits. Which of the following nerve roots were most likely damaged during delivery?
- A. C4 and C5
- B. C7 and C8
- C. C5 and C6 (Correct Answer)
- D. C8 and T1
- E. C6 and C7
Cervical dermatomes and myotomes Explanation: ***C5 and C6***
- The presentation of the infant's left arm being **pronated**, **medially rotated**, and unable to be moved away from the body is characteristic of **Erb-Duchenne palsy** (also called "waiter's tip" deformity).
- This condition results from damage to the **upper trunk of the brachial plexus**, specifically involving the **C5 and C6 nerve roots**.
- These roots innervate muscles responsible for **shoulder abduction** (deltoid, supraspinatus), **external rotation** (infraspinatus), and **elbow flexion/supination** (biceps brachii).
- The preserved wrist and digit function confirms the injury is limited to the upper trunk, sparing C7-T1.
*C4 and C5*
- While C5 is involved in Erb's palsy, the **C4 root** primarily contributes to the **phrenic nerve** (diaphragm innervation) and provides sensation to the neck and shoulder region.
- C4 does not significantly contribute to the brachial plexus motor function, so damage to C4 would not explain the shoulder and elbow deficits observed.
*C7 and C8*
- Damage to **C7 and C8** would primarily affect **wrist extension** (C7) and **finger flexion** (C8), not the shoulder abduction and elbow flexion deficits seen here.
- This pattern would be inconsistent with Erb's palsy and more suggestive of middle-to-lower trunk injury.
*C8 and T1*
- Injury to **C8 and T1** nerve roots causes **Klumpke's palsy**, affecting the **intrinsic hand muscles** and wrist flexors, leading to a "claw hand" deformity.
- The infant's preserved ability to move all wrists and digits rules out C8-T1 injury, as this would severely impair hand function and potentially cause **Horner's syndrome** (if T1 is involved).
*C6 and C7*
- While **C6** is involved in Erb's palsy, adding **C7** damage would extend the injury to affect **wrist extensors** (extensor carpi radialis) and **triceps** (elbow extension).
- The clinical presentation described is most consistent with isolated upper trunk (C5-C6) injury, not extended involvement of C7.
Cervical dermatomes and myotomes US Medical PG Question 10: A 3629-g (8-lb) newborn is examined shortly after spontaneous vaginal delivery. She was delivered at 40 weeks' gestation and pregnancy was uncomplicated. Her mother is concerned because she is not moving her left arm as much as her right arm. Physical examination shows her left arm to be adducted and internally rotated, with the forearm extended and pronated, and the wrist flexed. The Moro reflex is present on the right side but absent on the left side. Which of the following brachial plexus structures is most likely injured in this infant?
- A. Upper trunk (Correct Answer)
- B. Axillary nerve
- C. Lower trunk
- D. Long thoracic nerve
- E. Posterior cord
Cervical dermatomes and myotomes Explanation: ***Upper trunk***
- The symptoms described, including the arm being **adducted, internally rotated**, with the forearm extended and pronated, and a **flexed wrist**, are characteristic of **Erb-Duchenne palsy**, an injury to the **upper trunk** of the brachial plexus (C5-C6 nerve roots).
- The absence of the **Moro reflex** on the affected side further indicates an injury to the **upper brachial plexus**, as these roots contribute to the reflex arc.
*Axillary nerve*
- An injury to the **axillary nerve** would primarily affect the **deltoid** and **teres minor muscles**, leading to weakness in **shoulder abduction** and external rotation.
- While shoulder abduction is impaired in this case, the more widespread deficits affecting multiple arm movements point to a more proximal brachial plexus injury rather than an isolated axillary nerve lesion.
*Lower trunk*
- Injury to the **lower trunk** (C8-T1 nerve roots) typically results in **Klumpke's palsy**, characterized by weakness or paralysis of the **intrinsic hand muscles** and **flexors of the wrist and fingers**, leading to a "claw hand" deformity.
- The described presentation does not align with the classic features of Klumpke's palsy.
*Long thoracic nerve*
- An injury to the **long thoracic nerve** would cause **paralysis of the serratus anterior muscle**, leading to **scapular winging** (the medial border of the scapula protruding posteriorly, especially when pushing against a wall).
- This symptom is not described in the patient's presentation.
*Posterior cord*
- The **posterior cord** gives rise to the axillary and radial nerves. Injury to the posterior cord would affect muscles innervated by these nerves, including the **deltoid, triceps**, and **extensors of the wrist and fingers**.
- While some of these movements (e.g., forearm extension) are affected, the specific "waiter's tip" posture strongly points to an upper trunk injury, which involves a broader distribution of muscles than just those supplied by the posterior cord.
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