Carpal tunnel syndrome (CTS) is a peripheral neuropathy caused by chronic or acute compression of the median nerve by the transverse carpal ligament. It is characterized by both sensory disturbances (pain, tingling, and numbness) and motor symptoms (weakness and clumsiness of the thumb) in the area innervated by the median nerve distal to the carpal tunnel. Several occupational and non-occupational risk factors (e.g., manual labor, age, sex, diabetes) have been associated with the syndrome. The presence of clinical symptoms and signs of CTS (e.g., the hand elevation test, carpal compression test, and Phalen test) should raise suspicion, but the diagnosis must be confirmed with specific neurological tests (e.g., EMG, ENG). Conservative management (i.e., immobilization with a splint, local steroid injections, and ultrasound therapy) may be effective in patients who only experience mild to moderate symptoms. Surgical release of the transverse carpal ligament with decompression of the median nerve is indicated in acute cases or patients with moderate to severe symptoms (atrophy of the thenar eminence).
- Most common entrapment neuropathy in the upper extremity (90% of all cases) 
- The prevalence and yearly incidence of CTS may change according to several occupational and non-occupational factors.
Epidemiological data refers to the US, unless otherwise specified.
The following risk factors are associated with CTS: 
- Previous fracture of the distal radius (most important risk factor)
- Traumatic dislocation of the lunate
- Manual work; : increased risk in workers using vibrating tools or prolonged, forceful, and repetitive flexion/extension of the wrist 
- Rheumatoid arthritis and other types of chronic inflammation of the tendon sheaths 
- Pregnancy and puerperium; : hormone-mediated weight gain and edema of the wrist can narrow the carpal tunnel 
- Renal failure; : due to dialysis-associated deposition of amyloid 
- Diabetes with peripheral polyneuropathy
- Hypothyroidism 
- The carpal tunnel is a narrow fibro-osseous structure at the level of the palmar aspect of the wrist, delimited by the carpal bones and the transverse carpal ligament, which contains flexor tendons and the median nerve.
- Pressure increase within the carpal tunnel → compression of contained structures → impaired blood flow and altered microvascular structure of the median nerve → inflammatory reaction → edema and hypoxia → axonal degeneration 
Mild to moderate
- Symptoms develop in the areas innervated by the median nerve: palmar surface of the thumb, index, and middle fingers, and radial half of the ring finger. 
- Symptoms worsen at night.
- Usually, there is no loss of sensation of the palmar surface of the thenar eminence, because it is innervated by the superficial branch of the median nerve, which arises 5–7 cm proximal to the carpal tunnel and is, therefore, not compressed.
Sensory innervation of the thenar eminence is not affected in CTS.
Moderate to severe
Motor symptoms in addition to the symptoms mentioned above: 
- Weakened pinch and grip; : Patients often complain of dropping objects.
- Severe, sustained median nerve compression may lead to thenar atrophy and, subsequently, impaired thumb opposition.
Subtypes and variants
Tarsal tunnel syndrome 
- Definition: peripheral neuropathy caused by chronic or acute compression of the tibial nerve by the flexor retinaculum of the foot at the medial ankle
- Clinical features
There is no agreement as to which provocative test should be used to support the diagnosis of CTS. Several authors suggest combining two or more provocative tests to improve the specificity of the diagnosis. 
- Hand elevation test: : The hand is held above the head of the patient for approx. two minutes. The test is considered positive if the symptoms of CTS (paresthesia and numbness) are reproduced. This test is easy to perform in a clinical setting and has higher sensitivity and specificity than all other tests. 
- Carpal compression test: By applying moderate compression with the finger directly over the proximal edge of the carpal tunnel, the examiner may elicit paresthesia in the median nerve distribution.
- Phalen test: The examiner actively or passively holds the patient's wrist in full flexion (90°). The test is positive if paresthesia occurs or worsens in the areas innervated by the median nerve within one minute. This finding is considered highly specific (approx. 85%) for the diagnosis of CTS.
- Tinel sign: Percussion or tapping with the fingertips over the carpal tunnel leads to shooting pain and/or tingling in the areas innervated by the median nerve.
- Nerve conduction studies (NCS; confirmatory test): prolongation of the distal motor and sensory latency 
- Pattern of neurogenic disorder: abnormal spontaneous activity
- Decreased activity, potentials with large amplitude
There is strong evidence against the use of clinical signs alone to diagnose CTS because of their questionable sensitivity and specificity. Thus, electrodiagnostic studies (particularly NCS) are essential for diagnosis.
Mild to moderate symptoms 
- Conservative treatment
Moderate to severe symptoms (or no response to conservative treatment)
- Open or endoscopic release of the transverse carpal ligament