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Summary Table

Domain	Detail
Risk Factors	Women (3:1), pregnancy, hypothyroidism, diabetes mellitus, obesity, rheumatoid arthritis, acromegaly, repetitive wrist flexion/extension, dialysis-related amyloidosis
Etiology	Compression of the median nerve as it passes through the carpal tunnel at the wrist
Patient Presentation	Numbness, tingling, and pain in the first 3.5 digits (thumb, index, middle, and radial half of ring finger); symptoms worse at night; patient "shakes out" the hand for relief
Classic Physical Exam	Positive Tinel sign (tapping over the carpal tunnel reproduces paresthesias), positive Phalen maneuver (sustained wrist flexion for 60 seconds reproduces symptoms), thenar atrophy in advanced cases
Key Diagnostic Results	Nerve conduction study (NCS) / electromyography (EMG): prolonged distal sensory and motor latency of the median nerve across the wrist; decreased conduction velocity
Management	Mild: neutral wrist splinting (especially at night), NSAIDs. Moderate: corticosteroid injection into the carpal tunnel. Severe or refractory: surgical carpal tunnel release
Keywords	"Wakes up at night shaking her hand," "numbness in first three fingers," "thenar atrophy," "Tinel sign," "Phalen test," "drops objects," "pregnant woman with hand tingling"

1. Pathophysiology

The carpal tunnel is a narrow, rigid passageway on the palmar side of the wrist formed by the carpal bones dorsally and the transverse carpal ligament (flexor retinaculum) volarly. Nine flexor tendons and the median nerve pass through this space. Because the tunnel is inelastic, any process that increases the volume of its contents or decreases the space itself will compress the median nerve.

The median nerve carries both sensory and motor fibers. Its sensory distribution at the hand covers the palmar aspect of the first 3.5 digits (thumb, index, middle, and the radial half of the ring finger) and the corresponding fingertips. The motor branch, the recurrent thenar branch, innervates the thenar muscles (opponens pollicis, abductor pollicis brevis, and the superficial head of flexor pollicis brevis). This is why advanced compression produces thenar atrophy and weakness of thumb opposition and abduction.

The reason symptoms are worse at night relates to wrist position during sleep. Most people sleep with their wrists in a flexed posture, which narrows the tunnel further and increases intracarpal pressure. This explains why the patient classically reports waking up with numbness and needing to "shake the hand out" (the so-called flick sign) to regain sensation.

In pregnancy, fluid retention and generalized soft tissue edema increase intracarpal pressure. In hypothyroidism, mucopolysaccharide deposition thickens the synovial tissue. In diabetes, the nerve is more vulnerable due to underlying metabolic neuropathy. In rheumatoid arthritis, tenosynovial inflammation increases tunnel contents. In acromegaly, bony and soft tissue overgrowth narrows the space. Understanding these mechanisms is essential because exam vignettes frequently embed the underlying condition as a clue.

One critical anatomical nuance: the palmar cutaneous branch of the median nerve branches off proximal to the carpal tunnel and travels superficial to the flexor retinaculum. This means the palm itself is typically spared in carpal tunnel syndrome. If a patient has numbness over the thenar eminence of the palm, think of a more proximal median nerve lesion, not carpal tunnel.

2. Classification and Clinical Manifestation

Severity	Sensory Symptoms	Motor Findings	Electrodiagnostic Pattern
Mild	Intermittent numbness and tingling in the median nerve distribution; symptoms provoked by sustained wrist flexion/extension; nocturnal paresthesias	No weakness; no atrophy; grip strength preserved	Prolonged distal sensory latency only; motor latency normal
Moderate	Persistent numbness; decreased sensation to light touch and two-point discrimination in the median nerve territory	Mild weakness of thumb abduction and opposition; no visible atrophy yet	Prolonged distal sensory and motor latency; mild decrease in amplitude
Severe	Constant numbness; patient may report paradoxical improvement in pain (due to axonal loss)	Visible thenar atrophy; inability to oppose the thumb; difficulty with fine pinch grip; patient drops objects	Absent or severely attenuated sensory nerve action potentials; denervation changes (fibrillations, positive sharp waves) on EMG of thenar muscles

A commonly tested clinical pearl: patients with severe, long-standing CTS may report that their pain has actually decreased. This is not improvement. It reflects axonal degeneration where the nerve can no longer transmit pain signals. The presence of thenar atrophy in this context means the patient needs urgent surgical decompression, not conservative management.

3. Diagnostic Workup

Test	Role	Key Findings
Clinical examination (Tinel, Phalen, flick sign)	Best initial approach in the clinical setting	Tinel: tingling on tapping the volar wrist. Phalen: symptoms reproduced within 60 seconds of sustained wrist flexion. Flick sign: patient shakes hand for relief.
Nerve conduction study (NCS)	Most accurate / confirmatory test	Prolonged distal sensory latency of the median nerve (>3.5 ms); prolonged distal motor latency (>4.2 ms); decreased sensory nerve action potential amplitude
Electromyography (EMG)	Assesses severity (axonal damage)	Fibrillation potentials and positive sharp waves in the abductor pollicis brevis indicate denervation (severe CTS)
Ultrasound of the wrist	Adjunctive imaging	Cross-sectional area of the median nerve >10 mm² at the tunnel inlet is suggestive
MRI of the wrist	Rarely needed; used to identify structural causes	Useful when a space-occupying lesion (ganglion cyst, anomalous muscle) is suspected
X-ray of the wrist	Limited role	Considered only if bony abnormality suspected (e.g., prior fracture, osteoarthritis of the carpals)

The diagnosis of carpal tunnel syndrome is primarily clinical. In a straightforward vignette, a patient with classic symptoms plus a positive Tinel or Phalen test is enough to establish the diagnosis. You do not need electrodiagnostic testing to start initial management.

However, nerve conduction studies are the confirmatory gold standard. They are ordered when the clinical picture is ambiguous, when symptoms are atypical, when the patient fails conservative therapy and surgery is being considered, or when the examiner needs to distinguish CTS from cervical radiculopathy or other neuropathies. The hallmark finding is a prolonged distal sensory latency of the median nerve across the wrist. Sensory fibers are affected earlier and more prominently than motor fibers, which is why sensory latency prolongation is the most sensitive electrodiagnostic finding.

EMG is added to NCS when the clinician suspects axonal damage. Fibrillation potentials in the thenar muscles indicate denervation and correlate with a more severe and potentially irreversible injury. This distinction matters because it changes management: a patient with denervation on EMG should be referred for surgical release rather than continued conservative care.

When exam questions provide a vignette of a patient with wrist pain and numbness, look for these discriminating features before accepting CTS as the answer: (1) symptoms are in the median nerve territory, not the entire hand; (2) the dorsal hand is spared; (3) symptoms are worse at night or with sustained wrist flexion.

4. Management and Treatment

Stage	Intervention	Details
Initial / Mild	Neutral wrist splinting	Wrist held in neutral position (not flexed, not extended); worn primarily at night; recommended for at least 4 to 6 weeks
Initial / Mild	Activity modification	Avoid sustained wrist flexion/extension; ergonomic adjustments at the workplace
Initial / Mild	NSAIDs	Short-term symptom relief; limited long-term benefit for nerve compression
Moderate / Persistent	Corticosteroid injection	Local injection of methylprednisolone (typically 20 to 40 mg) into the carpal tunnel; provides temporary relief lasting weeks to months; can be repeated once
Severe / Refractory	Surgical carpal tunnel release	Division of the transverse carpal ligament; performed via open or endoscopic technique; definitive treatment
Pregnancy-related	Conservative management first	Most cases resolve spontaneously postpartum; splinting is first-line; corticosteroid injection if symptoms are debilitating; surgery rarely needed

The first-line treatment for mild to moderate CTS is neutral wrist splinting, especially worn during sleep. The neutral position (0 to 5 degrees of extension) minimizes intracarpal pressure. Patients should be instructed to wear the splint consistently for a minimum of 4 to 6 weeks before judging effectiveness. Activity modification and ergonomic counseling are added in parallel.

If splinting alone fails to provide adequate relief after 4 to 6 weeks, the next step is a corticosteroid injection into the carpal tunnel. This is performed by injecting just ulnar to the palmaris longus tendon at the level of the proximal wrist crease, directing the needle toward the ring finger. Methylprednisolone 20 to 40 mg mixed with 1 mL of lidocaine is standard. The injection often produces dramatic but temporary improvement; recurrence within 6 to 12 months is common. It can be repeated once, but if symptoms recur after two injections, surgical referral is indicated.

Surgical carpal tunnel release is the definitive treatment and is indicated for: (1) failure of conservative management after 3 to 6 months, (2) severe symptoms at presentation (thenar atrophy, constant numbness, denervation on EMG), or (3) acute median nerve compression (e.g., from a distal radius fracture). The surgery involves dividing the transverse carpal ligament, which permanently decompresses the tunnel. Success rates exceed 90%, though patients with severe axonal damage at the time of surgery may have incomplete recovery of motor function.

Oral corticosteroids are not recommended for CTS. Local injection is preferred because it delivers the drug directly to the site of compression with fewer systemic effects. In patients on anticoagulants, injection can still be performed with appropriate precautions but the bleeding risk must be weighed.

In pregnant patients, CTS often develops in the third trimester due to fluid retention and typically resolves within weeks to months after delivery. Conservative management (splinting, possibly a single corticosteroid injection for severe cases) is preferred. Surgery is almost never needed for pregnancy-related CTS.

5. Differential Diagnosis and Distractors

Differential	Why It Looks Similar	Key Discriminator
C6-C7 cervical radiculopathy	Numbness and tingling in the hand, may involve the index and middle fingers	Radiculopathy causes neck pain radiating down the arm; sensory loss follows a dermatomal pattern (not a peripheral nerve pattern); Spurling test is positive; deep tendon reflexes may be diminished; NCS of the median nerve at the wrist is normal
Pronator teres syndrome (proximal median nerve entrapment)	Median nerve territory symptoms identical to CTS	Numbness extends to the thenar eminence of the palm (palmar cutaneous branch is compressed because entrapment is proximal); pain is in the proximal forearm, not the wrist; Tinel sign is positive at the proximal forearm, not the wrist; no nocturnal worsening
Ulnar neuropathy at the elbow (cubital tunnel syndrome)	Hand numbness and weakness; patient drops objects	Symptoms involve the 4th and 5th digits (ulnar nerve territory); weakness of interossei and hypothenar muscles; Froment sign is positive; clawing of the ring and small fingers
Thoracic outlet syndrome	Arm numbness, tingling, and weakness	Symptoms worsen with arm elevation (e.g., Adson test, Roos stress test); involves the lower trunk of the brachial plexus (C8-T1); numbness in the medial forearm and hand (ulnar distribution); vascular symptoms (pallor, edema) may be present
Peripheral neuropathy (diabetic)	Numbness and tingling in the hands	Distribution is symmetric, stocking-glove pattern affecting both hands and feet; not limited to the median nerve territory; deep tendon reflexes are globally reduced; NCS shows diffuse abnormalities, not focal median nerve slowing
De Quervain tenosynovitis	Wrist pain, especially with gripping	Pain is on the radial (thumb) side of the wrist, not palmar; Finkelstein test is positive (pain with ulnar deviation while the thumb is clasped in a fist); no numbness or paresthesias
Raynaud phenomenon	Hand symptoms including tingling	Episodes involve color changes (white, blue, red) triggered by cold or stress; affects all fingers symmetrically (or asymmetrically in secondary Raynaud); no focal median nerve deficit

6. Traps and High-Yield Pearls

The single most common trap on this topic involves pattern recognition of the nerve distribution. The vignette will describe numbness in the hand, and students must resist choosing CTS if the symptoms involve the 4th and 5th digits (ulnar nerve) or the entire hand in a glove pattern (peripheral neuropathy). The examiners test whether you can map the complaint to the correct nerve territory. Always confirm that the symptoms are in the first 3.5 digits before selecting CTS.

A second frequent trap involves a patient with thenar atrophy who reports decreased pain. Students may interpret this as clinical improvement and choose continued conservative management. This is wrong. Loss of pain with progressive weakness indicates axonal death, and the correct next step is urgent surgical release.

Another tested concept is the pregnant patient with bilateral hand numbness. The examiner wants you to recognize that CTS in pregnancy is common, is driven by fluid retention, and is managed conservatively. The answer is wrist splinting, not surgery and not nerve conduction studies as a first step.

Watch for vignettes that introduce hypothyroidism as the underlying cause. If a patient has CTS in the setting of undiagnosed hypothyroidism (fatigue, weight gain, constipation, delayed relaxation of reflexes), the most important step is to check TSH and treat the thyroid disorder. CTS may resolve once the underlying condition is addressed.

Finally, remember the anatomy of the palmar cutaneous branch. If the vignette describes numbness over the thenar eminence of the palm in addition to the fingers, the lesion is proximal to the carpal tunnel (pronator teres syndrome or a more proximal median neuropathy), and CTS is the wrong answer.

The core competency being tested is the ability to localize a peripheral nerve lesion based on clinical findings, select the appropriate diagnostic and management sequence, and recognize when conservative therapy has failed and surgical intervention is required.

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