•. CASE 7

A 34-year-old diabetic woman complains of a 6-month history of progressive numbness and pain in her right hand that wakes her up at night. She states that her thumb is especially affected. She says that she is beginning to drop objects she is carrying in her right hand. She denies a history of trauma, exposure to heavy metals, or a family history of multiple sclerosis. The only medication she takes is an oral hypoglycemic agent.

• What is the most likely diagnosis?

• What is the mechanism of the disorder?

• What is your next step?

ANSWERS TO CASE 7: Carpal Thnnel Syndrome

Summary: A 34-year-old diabetic woman complains of a 6-month history of progressive numbness and pain in her right hand occurring especially at nighttime and affecting her thumb. She states that she is beginning to drop objects she carries in her right hand.

• Most likely diagnosis: Carpal tunnel syndrome.

• Mechanism of the disorder: Median nerve compression.

O Next step in therapy: Nighttime splint and nonsteroidal anti- inflammatory drugs (NSAIDs).

Analysis

Objectives

1. Know the clinical presentation, pathophysiology, and risk factors for carpal tunnel syndrome.

2. Know the medical and surgical options for treating carpal tunnel syndrome.

Considerations

The distribution of the progressive numbness and pain is suggestive of median nerve compression. In addition, exacerbation of the patient’s symptoms at night is typical of carpal tunnel syndrome. The mechanism of this disorder is compression of the median nerve as it passes within the carnal tunnel. This causes axonal damage and narrowing of the nerve. Median nerve compression causes numbness and pain in the thumb, index finger. and middle and lateral aspects of the ring finger. The median nerve may be compressed anywhere along its length from the brachial plexus down to the hand, but the most common site of compression is within the carnal tunnel, where it is dorsal to the transverse carnal ligament. The carpal canal is a rigid structure that causes physiologic dysfunction by producing median nerve ischemia. The best initial management is a nighttime splint for the wrist and avoidance of excess activity with the hand.

APPROACH TO CARPAL TUNNEL SYNDROME

Definitions

Carpal tunnel syndrome: Median nerve compression at the wrist leading to paresthesias of the radial three fingers and sometimes hand weakness.

Tinel’s sign: Reproduction of the patient’s symptoms by percussion of the median nerve at the wrist.

Electrophysiologic studies: Investigation of nerve conduction and muscle innervation.

Clinica’ Approach

The carpal canal serves as a mechanical conduit for the digital flexor tendons. The walls and tloor on the dorsal surface of the canal are formed by the carpal bones, and the ventral aspect is confined by the strong, inelastic, transverse carpal ligament. The smallest cross-sectional area of the canal is created by extremes of flexion and extension of the wrist (Figure 7—I). Exacerbation of symptoms at night is thought to be caused by edema: tenosynovitis may also be present. Carpal tunnel syndrome is associated with endocrine conditions, diabetes. myxedema, hyperthyroidism, acromegaly, and pregnancy. Other causes are autoimmune disorders, lipomas of the canal, bone abnormalities, and hematomas. The etiology is often multifactorial. Women are more commonly atiected in a ratio of approximately 3: 1.

The diagnosis of carpal tunnel syndrome is clinical, and the symptoms are typical. The exertion of direct digital pressure by the examiner over the median nerve at the carpal tunnel frequently reproduces the symptoms in approximately 30 seconds. In the Phalen maneuver, gravity-induced wrist flexion also produces the classic symptoms of this condition. A positive Tinel’s sign is present when direct percussion over the nerve reproduces paresthesia. Sensory loss, particularly vibration sense, and motor loss may be present with thenar muscle wasting and decreased abductor muscle resistance. Electrophysiologic studies may be helpful. A comparison of median and ulnar or median and radial sensory stimulation valties at the wrist is useful in confirming the diagnosis. Radiographs, including a “carpal tunnel view.” are recommended to detect arthritis or fractures. Computed tomography and magnetic resonance imaging are rarely needed.

Conservative therapy consists of the use of splints and nonsteroidal anti- inflammatory agents. Splints should be light and hold the wrist in a neutral or slightly extended position. Local steroid injections are effective in 80% to 90% of patients, but symptoms tend to return after months or sometimes years. Injections should not be given more frequently than on two or three occasions per year. Care must be taken not to inject directly into the median nerve. Surgery is indicated for intractable symptoms that are refractory to medical management. It consists of complete division of the transverse carpal ligament extending distally from the ulnar side of the median nerve. The results of surgery are generally good. Poor results are usually associated with either a mis- diagnosis or failure to divide the ligament completely. The surgery can be performed with an open or an endoscopic approach. A tourniquet is used to exsanguinate the limb, and the operative field is infiltrated with a local anesthetic agent such as Xylocaine; in addition, intravenous sedation can be used. The Palmer fascia and the ligament are divided vertically from the proximal end of the carpal tunnel to its most distal point, and a wide separation of the ends of the ligament is observed (Figure 7—2). The underlying median nerve is carefully protected. A small tissue flap is left attached to the hook of the hamate. and the skin is closed. Postoperatively, the wrist is splinted in slight extension for approximately 2 weeks.

The potential advantages of the endoscopic approach are less discomfort. minimal scarring, a shorter period of immobilization, and a more rapid recovery. Persistent or recurrent symptoms should be investigated by repeated electrophysiologic studies and by exclusion of other causes of nerve compression. Occasionally. the ulnar nerve is compressed at the wrist, but more commonly, compression of this nerve occurs in the fibromuscular groove posterior to the medial epicondyle.

Comprehension Questions

L7.l1 A 24-year-old medical student notes some numbness and tingling of her right hand. She states that primarily her little finger is affected. Which of the following is the most likely etiology?

A. Median nerve

B. Radial nerve

C. Ulnar nerve

D. Long thoracic nerve

L7.21 Which of the following is most likely to be a risk factor for the development of carpal tunnel syndrome?

A. Diabetes insipidus

B. Hypothyroidism

C. Addison’s syndrome

D. Fibromyalgia

Answers

[7.11 C. The sensory innervation of the little finger and the ulnar side of the ring finger is achieved with the ulnar nerve.

L7.21 B. Hypothyroidism (as well as diabetes mellitus, hyperthyroidism, pregnancy, and acromegaly) is associated with carpal tunnel syndrome.

CLINICAL PEARLS

+ Carpal tunnel syndrome usually involves pain to the radial three

fingers. especially at night.

The initial treatment of carpal tunnel syndrome includes adminis

tration of NSAIDs and the use of a wrist splint.

.:. Surgery is indicated when severe pain or progressive motor weakness occurs despite conservative measures.