Dermatomes and myotomes

Dermatomes and myotomes US Medical PG Question 1: A 50-year-old man arrives to the clinic complaining of progressive weakness. He explains that for 3 months he has had difficulty climbing the stairs, which has now progressed to difficulty getting out of a chair. He denies diplopia, dysphagia, dyspnea, muscle aches, or joint pains. He denies weight loss, weight gain, change in appetite, or heat or cold intolerance. He reports intermittent low-grade fevers. He has a medical history significant for hypertension and hyperlipidemia. He has taken simvastatin and losartan daily for the past 6 years. His temperature is 99.0°F (37.2°C), blood pressure is 135/82 mmHg, and pulse is 76/min. Cardiopulmonary examination is normal. The abdomen is soft, non-tender, non-distended, and without hepatosplenomegaly. Muscle strength is 3/5 in the hip flexors and 4/5 in the deltoids, biceps, triceps, patellar, and Achilles tendon reflexes are 2+ and symmetric. Sensation to pain, light touch, and vibration are intact. Gait is cautious, but grossly normal. There is mild muscle tenderness of his thighs and upper extremities. There is no joint swelling or erythema and no skin rashes. A complete metabolic panel is within normal limits. Additional lab work is obtained as shown below: Serum: Na+: 141 mEq/L Cl-: 100 mEq/L K+: 4.3 mEq/L HCO3-: 23 mEq/L Urea nitrogen: 18 mg/dL Glucose: 128 mg/dL Creatinine: 1.0 mg/dL Alkaline phosphatase: 69 U/L Aspartate aminotransferase (AST): 302 U/L Alanine aminotransferase (ALT): 210 U/L TSH: 6.9 uU/mL Thyroxine (T4): 5.8 ug/dL Creatine kinase: 4300 U/L C-reactive protein: 11.9 mg/L Erythrocyte sedimentation rate: 37 mm/h Which of the following is the most accurate diagnostic test?

• A. Statin cessation
• B. Muscle biopsy (Correct Answer)
• C. Autoantibodies
• D. Electromyography
• E. Fine needle aspiration

Dermatomes and myotomes Explanation: ***Muscle biopsy*** - A **muscle biopsy** is the **most accurate diagnostic test** for establishing the definitive diagnosis of myopathy in this patient with **proximal muscle weakness** and markedly elevated **creatine kinase (CK 4300 U/L)**. - While the patient is on long-term statin therapy, the **persistently elevated inflammatory markers** (ESR 37, CRP 11.9) and very high CK raise concern for **statin-associated immune-mediated necrotizing myopathy (IMNM)**, not just simple statin myopathy. - Muscle biopsy can differentiate between **toxic statin myopathy** (which shows minimal inflammation) and **immune-mediated necrotizing myopathy** (which shows necrosis with minimal or patchy inflammatory infiltrates). - This distinction is **clinically critical** because IMNM requires **immunosuppressive therapy** in addition to statin discontinuation, whereas simple statin myopathy resolves with drug cessation alone. *Statin cessation* - While **stopping the statin** is an important **management step**, it is a **therapeutic intervention**, not a diagnostic test. - The question specifically asks for the "most accurate **diagnostic test**," making this an inappropriate answer despite being good clinical practice. - In cases of suspected statin-associated IMNM, simply stopping the statin may not resolve symptoms, necessitating a definitive diagnosis. *Autoantibodies* - **Anti-HMGCR antibodies** are highly specific for statin-associated immune-mediated necrotizing myopathy and would support the diagnosis. - However, **muscle biopsy** remains the **gold standard** as it provides direct histopathologic confirmation and can identify the pattern of muscle injury. - Autoantibody testing would be complementary but not as definitive as tissue diagnosis. *Electromyography* - **EMG** can confirm a **myopathic pattern** (short-duration, low-amplitude motor unit potentials) and help exclude neurogenic causes. - However, it is a **functional test** that shows abnormal electrical activity but does not provide the **specific histopathologic diagnosis** that muscle biopsy offers. - EMG findings are supportive but not definitive for the underlying etiology. *Fine needle aspiration* - **Fine needle aspiration** is used for cytological examination of masses or lymph nodes to diagnose malignancy or infection. - It is **not applicable** to the diagnosis of myopathy or muscle weakness and would not provide useful information in this clinical scenario.

Dermatomes and myotomes US Medical PG Question 2: A 25-year-old man comes to the physician for severe back pain. He describes the pain as shooting and stabbing. On a 10-point scale, he rates the pain as a 9 to 10. The pain started after he lifted a heavy box at work; he works at a supermarket and recently switched from being a cashier to a storekeeper. The patient appears to be in severe distress. Vital signs are within normal limits. On physical examination, the spine is nontender without paravertebral muscle spasms. Range of motion is normal. A straight-leg raise test is negative. After the physical examination has been completed, the patient asks for a letter to his employer attesting to his inability to work as a storekeeper. Which of the following is the most appropriate response?

• A. “Yes. Since work may worsen your condition, I would prefer that you stay home a few days. I will write a letter to your employer to explain the situation.”
• B. You say you are in severe pain. However, the physical examination findings do not suggest a physical problem that can be addressed with medications or surgery. I'd like to meet on a regular basis to see how you're doing.
• C. I understand that you are uncomfortable, but the findings do not match the severity of your symptoms. Let's talk about the recent changes at your job. (Correct Answer)
• D. The physical exam findings do not match your symptoms, which suggests a psychological problem. I would be happy to refer you to a mental health professional.
• E. The physical exam findings suggest a psychological rather than a physical problem. But there is a good chance that we can address it with cognitive-behavioral therapy.

Dermatomes and myotomes Explanation: ***"I understand that you are uncomfortable, but the findings do not match the severity of your symptoms. Let's talk about the recent changes at your job."*** - This response acknowledges the patient's reported discomfort while gently highlighting the **discrepancy between symptoms and objective findings**, which is crucial in cases of suspected **somatoform or functional pain**. - It also opens communication about potential **psychosocial stressors** related to his job change, which could be contributing to his symptoms, without dismissing his pain or making a premature diagnosis. *"You say you are in severe pain. However, the physical examination findings do not suggest a physical problem that can be addressed with medications or surgery. I'd like to meet on a regular basis to see how you're doing."* - While this option correctly identifies the lack of physical findings, it can be perceived as dismissive of the patient's pain, potentially damaging the **physician-patient relationship**. - Suggesting regular meetings without a clear plan for addressing his immediate concerns or exploring underlying issues might not be the most effective initial approach. *“Yes. Since work may worsen your condition, I would prefer that you stay home a few days. I will write a letter to your employer to explain the situation.”* - This response would **validate the patient's claim of severe pain** without objective evidence, potentially reinforcing illness behavior and avoiding addressing the underlying issue. - Providing a doctor's note for inability to work without a clear diagnostic basis or understanding of the pain's origin is **medically inappropriate** and could set a precedent for future such requests. *"The physical exam findings do not match your symptoms, which suggests a psychological problem. I would be happy to refer you to a mental health professional."* - Directly labeling the problem as "psychological" can be **stigmatizing and alienating** to the patient, leading to distrust and resistance to care. - While a psychological component might be present, immediately referring to mental health without further exploration of the patient's situation or current stressors is premature and lacks empathy. *"The physical exam findings suggest a psychological rather than a physical problem. But there is a good chance that we can address it with cognitive-behavioral therapy."* - Similar to the previous option, explicitly stating a "psychological problem" can be **stigmatizing**. - Jumping directly to recommending **cognitive-behavioral therapy (CBT)** without a comprehensive discussion and patient buy-in is premature and may lead to non-compliance.

Dermatomes and myotomes US Medical PG Question 3: A 78-year-old woman is accompanied by her family for a routine visit to her primary care provider. The family states that 5 months prior, the patient had a stroke and is currently undergoing physical therapy. Today, her temperature is 98.2°F (36.8°C), blood pressure is 112/72 mmHg, pulse is 64/min, and respirations are 12/min. On exam, she is alert and oriented with no deficits in speech. Additionally, her strength and sensation are symmetric and preserved bilaterally. However, on further neurologic testing, she appears to have some difficulty with balance and a propensity to fall to her right side. Which of the following deficits does the patient also likely have?

• A. Hemiballismus
• B. Hemispatial neglect
• C. Intention tremor
• D. Contralateral eye deviation
• E. Truncal ataxia (Correct Answer)

Dermatomes and myotomes Explanation: ***Truncal ataxia*** - This patient's symptoms of **difficulty with balance** and a **propensity to fall to her right side** are highly suggestive of truncal ataxia. - While she had a stroke, her preserved speech, symmetric strength and sensation, and alertness rule out typical hemiparesis or aphasia, pointing towards a **cerebellar lesion** affecting balance and coordination. *Hemiballismus* - This condition involves **flailing, high-amplitude, involuntary movements** typically affecting one side of the body. - The patient's description of balance issues and falling, without mention of such specific movements, makes hemiballismus less likely. *Hemispatial neglect* - Characterized by the **inability to attend to one side of the environment**, usually the left side following a right parietal stroke. - The patient's presentation does not describe an indifference to one side of her visual or personal space. *Intention tremor* - An **intention tremor** is a tremor that worsens during purposeful movement towards a target. - While it can be associated with cerebellar dysfunction, the primary deficit described is imbalance and falling to one side, not specifically a tremor. *Contralateral eye deviation* - This typically occurs in acute stroke scenarios as part of a **gaze preference**, where the eyes deviate towards the side of the lesion (or away from the hemiparesis). - The patient is 5 months post-stroke and is alert with no acute focal deficits, making acute eye deviation unlikely as a chronic presenting symptom here.

Dermatomes and myotomes US Medical PG Question 4: A 41-year-old woman presents with back pain for the past 2 days. She says that the pain radiates down along the posterior right thigh and leg. She says the pain started suddenly after lifting a heavy box 2 days ago. Past medical history is irrelevant. Physical examination reveals a straight leg raise (SLR) test restricted to 30°, inability to walk on her toes, decreased sensation along the lateral border of her right foot, and diminished ankle jerk on the same side. Which of the following nerve roots is most likely compressed?

• A. Fourth lumbar nerve root (L4)
• B. Second sacral nerve root (S2)
• C. Third sacral nerve root (S3)
• D. Fifth lumbar nerve root (L5)
• E. First sacral nerve root (S1) (Correct Answer)

Dermatomes and myotomes Explanation: ***First sacral nerve root (S1)*** - **Inability to walk on toes** (weakness of gastrocnemius and soleus), **decreased sensation along the lateral border of the foot**, and a **diminished ankle jerk** are classic signs of S1 radiculopathy. - The radiating pain down the posterior leg, restricted straight leg raise due to a sudden onset after lifting, points towards a **disc herniation** compressing the S1 nerve root. *Fourth lumbar nerve root (L4)* - Compression of L4 typically causes **weakness in knee extension** (quadriceps), diminished patellar reflex, and sensory loss over the medial aspect of the shin. - The patient's symptoms (inability to walk on toes, diminished ankle jerk) are not consistent with L4 nerve root involvement. *Second sacral nerve root (S2)* - S2 radiculopathy primarily affects sensation in the posterior thigh and calf and can cause **weakness in knee flexion** and **plantarflexion**, but the complete constellation of symptoms (especially ankle jerk reflex) is more indicative of S1. - Isolated S2 compression without S1 involvement is less common with these specific signs. *Third sacral nerve root (S3)* - S3 nerve root compression typically presents with **perineal numbness** and issues with bowel or bladder function due to its involvement in these functions. - The described motor and sensory deficits are not characteristic of S3 radiculopathy. *Fifth lumbar nerve root (L5)* - L5 radiculopathy is characterized by **weakness in foot dorsiflexion** (foot drop) and toe extension, leading to inability to walk on heels, and sensory loss on the dorsum of the foot. - While L5 compression can cause radiating pain and a restricted straight leg raise, the specific deficit of **inability to walk on toes** and a **diminished ankle jerk** are not typical of L5 involvement.

Dermatomes and myotomes US Medical PG Question 5: A 22-year-old man is rushed to the emergency department after a motor vehicle accident. The patient states that he feels weakness and numbness in both of his legs. He also reports pain in his lower back. His airway, breathing, and circulation is intact, and he is conversational. Neurologic exam is significant for bilateral lower extremity flaccid paralysis and impaired pain and temperature sensation up to T10-T11 with normal vibration sense. A computerized tomography scan of the spine is performed which shows a vertebral burst fracture of the vertebral body at the level of T11. Which of the following findings is most likely present in this patient?

• A. Intact vibration sense
• B. Bowel incontinence (Correct Answer)
• C. Flaccid paralysis at the level of the lesion
• D. Spasticity below the lesion
• E. Impaired proprioception sense

Dermatomes and myotomes Explanation: ***Bowel incontinence*** - The presented symptoms of acute **bilateral lower extremity flaccid paralysis**, **impaired pain and temperature sensation**, and a T11 **vertebral burst fracture** are highly indicative of **anterior cord syndrome**. - **Anterior cord syndrome** characteristically involves damage to the **anterior two-thirds of the spinal cord**, affecting the **corticospinal tracts** (motor control), **spinothalamic tracts** (pain and temperature sensation), and the **autonomic fibers** that control bladder and bowel function, leading to **bowel and bladder dysfunction**. *Intact vibration sense* - The sensation of **vibration** and **proprioception** is carried by the **dorsal columns** (posterior part of the spinal cord), which are typically **spared** in **anterior cord syndrome**. - Therefore, **intact vibration sense** is an expected finding, but the question asks for the **most likely finding** that represents a significant complication of the syndrome. *Flaccid paralysis at the level of the lesion* - While **flaccid paralysis** is present in the lower extremities, it occurs **below the level of the lesion** due to damage to the descending motor tracts (corticospinal tracts). - Flaccid paralysis *at* the level of the lesion would typically involve damage to the **lower motor neurons** at that specific segment, which is not the primary feature described for a burst fracture causing **anterior cord syndrome**. *Spasticity below the lesion* - **Spasticity** typically develops much **later** in spinal cord injuries, after the initial phase of **spinal shock** resolves (usually weeks to months). - In the acute phase following a significant spinal cord injury, **flaccid paralysis** is the more common finding below the lesion, reflecting spinal shock. *Impaired proprioception sense* - Similar to vibration sense, **proprioception** is primarily mediated by the **dorsal columns**, which are generally **spared** in **anterior cord syndrome**. - Therefore, **proprioception** would likely be **intact**, not impaired, in this specific type of spinal cord injury.

Dermatomes and myotomes US Medical PG Question 6: You are seeing an otherwise healthy 66-year-old male in clinic who is complaining of localized back pain and a new rash. On physical exam, his vital signs are within normal limits. You note a vesicular rash restricted to the upper left side of his back. In order to confirm your suspected diagnosis, you perform a diagnostic test. What would you expect to find on the diagnostic test that was performed?

• A. Gram negative bacilli
• B. Branching pseudohyphae
• C. Pear shaped motile cells
• D. Multinucleated giant cells (Correct Answer)
• E. Gram positive cocci

Dermatomes and myotomes Explanation: ***Multinucleated giant cells*** - The patient's presentation of a **unilateral, vesicular rash** in an older adult, along with localized back pain, is highly suggestive of **herpes zoster (shingles)**. - A Tzanck smear, a common diagnostic test for vesicular lesions, would reveal **multinucleated giant cells** and **intranuclear inclusions**, characteristic cytopathic effects of herpesviruses like VZV. *Gram negative bacilli* - This finding would suggest a **bacterial infection**, typically not associated with vesicular rashes like shingles. - Gram-negative bacilli are often implicated in conditions such as **urinary tract infections** or **sepsis**, not dermatological viral infections. *Branching pseudohyphae* - This microscopic feature is characteristic of **fungal infections**, specifically **Candida species**, which present as a candidiasis rash, not a dermatomal vesicular rash. - Fungal rashes are typically erythematous and can be pruritic but do not usually form discrete vesicles in a dermatomal distribution. *Pear shaped motile cells* - This describes **Trichomonas vaginalis**, a parasite causing sexually transmitted infections, primarily **vaginitis** or **urethritis**. - This finding would be completely unrelated to a vesicular skin rash or the suspected diagnosis of shingles. *Gram positive cocci* - This finding is indicative of a **bacterial infection**, such as those caused by **Staphylococcus aureus** or **Streptococcus pyogenes**. - While these bacteria can cause skin infections (e.g., impetigo, cellulitis), they do not produce the classic unilateral vesicular rash of shingles and would not involve multinucleated giant cells on microscopy.

Dermatomes and myotomes US Medical PG Question 7: A 67-year-old man comes to the physician because of progressive burning pain and intermittent "electrical shocks" in his right chest for 3 months. Over the last 2 weeks, the pain has increased to an extent that he can no longer tolerate clothing on the affected area. Three months ago, he had a rash around his right nipple and axilla that resolved a week later. The patient had a myocardial infarction 2 years ago. He has smoked one pack of cigarettes daily for 47 years. Current medications include aspirin, simvastatin, metoprolol, and ramipril. His temperature is 36.9°C (97.9°F), pulse is 92/min, and blood pressure is 150/95 mm Hg. Examination shows increased sensation to light touch over the right chest. The remainder of the physical examination shows no abnormalities. Which of the following is the most appropriate next step in management?

• A. Sublingual nitrates
• B. Oral famciclovir
• C. Intrathecal glucocorticoids
• D. Oral tricyclic antidepressants
• E. Oral gabapentin (Correct Answer)

Dermatomes and myotomes Explanation: ***Oral gabapentin*** - The patient's presentation with a history of a unilateral vesicular rash followed by persistent, burning pain, "electrical shocks," and **allodynia** (increased sensation to light touch) in the same dermatomal distribution is highly characteristic of **postherpetic neuralgia (PHN)**. - **Gabapentin** (and pregabalin) are first-line medications for neuropathic pain conditions like PHN as they modulate calcium channels in the central nervous system, reducing neurotransmitter release. *Sublingual nitrates* - Sublingual nitrates are used for immediate relief of **anginal chest pain**, which is typically described as pressure or heaviness, often radiating to the arm or jaw, and relieved by rest or nitrates. - The described pain is neuropathic (burning, electrical shocks, allodynia) and does not fit the pattern of angina, despite the patient's history of MI. *Oral famciclovir* - **Famciclovir** (and acyclovir, valacyclovir) are antiviral medications used to treat acute **herpes zoster (shingles)** to shorten the duration of the rash and reduce the risk of PHN if given within 72 hours of rash onset. - The patient's rash resolved 3 months ago, meaning the acute viral phase is over, and antiviral therapy at this stage would not be effective for PHN. *Intrathecal glucocorticoids* - **Intrathecal glucocorticoids** are rarely used for PHN and are generally reserved for severe, refractory cases as a last resort due to potential side effects and invasiveness. - They are not a first-line treatment for PHN, especially before trying oral neuropathic pain medications. *Oral tricyclic antidepressants* - **Tricyclic antidepressants (TCAs)** like amitriptyline are effective for neuropathic pain, including PHN, and are considered first-line agents alongside gabapentinoids. - However, in elderly patients with a history of cardiac disease (MI, hypertension, on metoprolol and ramipril), TCAs carry a higher risk of **cardiac side effects** (e.g., arrhythmias, orthostatic hypotension) and anticholinergic side effects compared to gabapentin.

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)

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.

Dermatomes and myotomes US Medical PG Question 9: A 57-year-old man presents to the ED complaining of back and left leg pain. He was lifting heavy furniture while helping his daughter move into college when all of sudden he felt a sharp pain at his back. The pain is described as severe, worse with movement, and shoots down his lateral thigh. The patient denies any bowel/urinary incontinence, saddle anesthesia, weight loss, or weakness. He denies any past medical history but endorses a family history of osteoporosis. He has been smoking 1 pack per day for the past 20 years. Physical examination demonstrated decreased sensation at the left knee, decreased patellar reflex, and a positive straight leg test. There is diffuse tenderness to palpation at the lower back but no vertebral step-offs were detected. What is the most likely etiology for this patient’s pain?

• A. Vertebral compression fracture
• B. Disc herniation at the L4/L5 vertebra
• C. Spinal metastasis from lung cancer
• D. Disc herniation at the L3/L4 vertebra (Correct Answer)
• E. Lumbar muscle sprain

Dermatomes and myotomes Explanation: ***Disc herniation at the L3/L4 vertebra*** - The patient's symptoms of **acute back pain radiating down the lateral thigh** after lifting, combined with **decreased sensation at the left knee** and a **decreased patellar reflex**, are classic signs of L3/L4 nerve root compression. - A **positive straight leg test** also supports nerve root irritation, and the absence of red flag symptoms like incontinence or saddle anesthesia makes a simple disc herniation more likely than other serious conditions. *Vertebral compression fracture* - While lifting heavy objects can cause compression fractures, these usually present with more **severe, localized pain** that is not typically radiating with specific dermatomal or reflex changes. - Absence of **vertebral step-offs** or significant predisposing factors for a fracture (e.g., severe osteoporosis, trauma) makes this less likely given the specific neurological findings. *Disc herniation at the L4/L5 vertebra* - An L4/L5 disc herniation would typically cause symptoms related to the **L5 nerve root**, such as pain radiating down the **lateral leg into the foot**, **weakness in dorsiflexion of the ankle** or **big toe**, and potentially a **decreased medial hamstring reflex**. - The patient's reported symptoms (lateral thigh pain, decreased knee sensation, decreased patellar reflex) are more consistent with **L4 nerve root** involvement. *Spinal metastasis from lung cancer* - Although the patient has a **smoking history** and could be at risk for lung cancer, this diagnosis typically presents with more **insidious onset** of unexplained back pain, often with **weight loss**, and sometimes with more profound neurological deficits or bone pain not relieved by rest. - The acute onset after an inciting event and specific neurological findings of a single nerve root are less suggestive of metastasis. *Lumbar muscle sprain* - A muscle sprain would typically present with **localized back pain**, often worsened by movement, but would **not involve radicular pain** shooting down the leg, nor would it cause specific **neurological deficits** like decreased sensation or reflex changes. - The positive straight leg test and neurological findings rule out a simple muscle sprain.

Dermatomes and myotomes US Medical PG Question 10: A 48-year-old male presents to his primary care provider with a two-week history of low back pain and left leg pain. He reports that his symptoms started while he was working at his job as a construction worker. He has since experienced intermittent achy pain over his lumbar spine. He has also noticed pain radiating into his left leg and weakness in left ankle dorsiflexion. On exam, he demonstrates the following findings on strength testing of the left leg: 5/5 in knee extension, 4/5 in ankle dorsiflexion, 4/5 in great toe extension, 5/5 in ankle plantarflexion, and 5/5 in great toe flexion. The patellar reflexes are 5/5 bilaterally. He is able to toe walk but has difficulty with heel walking. Weakness in which of the following compartments of the leg is most likely causing this patient’s foot drop?

• A. Lateral compartment
• B. Superficial posterior compartment
• C. Deep posterior compartment
• D. Anterior compartment (Correct Answer)
• E. Medial compartment

Dermatomes and myotomes Explanation: ***Anterior compartment*** - Weakness in **ankle dorsiflexion** and **great toe extension**, coupled with difficulty **heel walking**, indicates a foot drop due to dysfunction of muscles in the anterior compartment, such as the **tibialis anterior**, **extensor hallucis longus**, and **extensor digitorum longus**. - These muscles are primarily innervated by the **deep fibular nerve**, which is susceptible to compression from conditions like **lumbar radiculopathy** (L4-L5 nerve root involvement). *Lateral compartment* - Muscles in the lateral compartment (**fibularis longus** and **brevis**) are responsible for **eversion** of the foot. - Weakness in this compartment would manifest as difficulty everting the foot, not primarily ankle dorsiflexion or great toe extension deficits. *Superficial posterior compartment* - This compartment contains muscles like the **gastrocnemius** and **soleus**, which are primarily responsible for **ankle plantarflexion**. - The patient exhibits 5/5 strength in ankle plantarflexion and is able to toe walk, indicating these muscles are functioning well. *Deep posterior compartment* - Muscles in the deep posterior compartment (**tibialis posterior**, **flexor digitorum longus**, **flexor hallucis longus**) are involved in **inversion** and **toe flexion**. - The patient has 5/5 strength in great toe flexion, suggesting intact function of these muscles, and his primary deficit is in dorsiflexion. *Medial compartment* - There is no distinct "medial compartment" of the leg in the anatomical sense comparable to the other listed compartments; rather, various muscles contribute to medial actions. - The symptoms described specifically point to weakness in dorsiflexion and toe extension, localizing the problem to the anterior compartment.

Dermatomes and myotomes Flashcard 1 of 7

Question: What dermatome is found at the posterior half of the skull? _____

Answer: C2

Dermatomes and myotomes Flashcard 2 of 7

Question: Which type of sensory receptor is found on finger tips and superficial skin? _____

Answer: Merkel discs

Dermatomes and myotomes Flashcard 3 of 7

Question: ID Structure: _____

Answer: Main sensory nucleus of V

Dermatomes and myotomes Flashcard 4 of 7

Question: ID Structure: _____

Answer: Medial lemniscus

Dermatomes and myotomes Flashcard 5 of 7

Question: What dermatome is found at the inguinal ligament? _____

Answer: L1

Dermatomes and myotomes Flashcard 6 of 7

Question: What dermatome includes the thumbs? _____

Answer: C6

Dermatomes and myotomes Flashcard 7 of 7

Question: What syndrome is associated with lesion of the following areas? _____1. Corticospinal tract2. Medial lemniscus3. Hypoglossal nerve (CN XII)

Answer: Medial medullary syndrome (Inferior alternating hemiplegia)