Carpal tunnel syndrome, a relatively common condition, is usually characterized in the early stages by pain and paresthesia or tingling in the first three fingers. This distribution of symptoms is classic, although occasionally the fourth and fifth fingers may be involved as well. The pain or paresthesia often is nocturnal (occurs at night) and may radiate upwards into the arm, which may be confused with C5/C6 radiculopathy (pinched nerve in the neck). The diagnosis is confirmed by electromyogram (EMG) and the measurement of nerve conduction velocities (NCVs) which show a slowed conduction of the median nerve at the wrist.
The carpal tunnel syndrome is a result of mechanical compression of the median nerve as it runs through the tunnel formed by the carpal bones, flexor tendons, and transverse volar carpal ligament. There are several causes of this condition. In the acute type, the compression is caused by acute swelling of the flexor tendons occasioned by unaccustomed exercise such as painting walls or keeping the wrist in an extended position such as in cycling. In the chronic type the compression is caused by hypertrophy of the tendons caused by continuous exertion such as typing or using a computer. This "occupational type" is usually caused by a combination of both the acute and chronic muscle types. Additional causes of the chronic type is the hypertrophy of carpal ligaments or arthritic changes in the carpal bones in the elderly or a deposit of various substances into the sheath's of the tendons such as in amyloid or chronic dialysis. The relief of compression by a surgical section of the ligament is the treatment of choice for the chronic type while the acute type is treated with rest, splints and medications, including a short course of steroids. The mechanical compression of the median nerve at the carpal tunnel as the cause of gradual atrophy of thenar muscles, with subjective numbness without objective sensory loss, was demonstrated at autopsy by Marie and Foix in 1913. Learmonth, probably, was the first to decompress the median nerve in 1933 in an attempt to relieve such symptoms. It was Sutherland, however, who presented convincing evidence that in most cases it is not direct compression of the nerve but rather the compression of the vascular structures of the nerve that leads to edema, to protein exudation, and eventually to fibrosis, and is responsible for the neurological symptoms. His concept particularly is important because it explains both the nature and the gradual progression of the symptoms so commonly seen in patients with carpal tunnel syndrome, and it presents a strong rationale for early surgical decompression.
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In the carpal tunnel, the median nerve particularly is vulnerable to compression as it runs between the retinaculum on one side and the unyielding bone structures on the other. According to Sutherland, in the earliest stages the compression of the venous outflow from the median nerve leads to hyperemia,. general circulatory slowing, and congestion in the epineural and intrafunicular tissues. This further increases the pressure within the carpal tunnel and eventually leads to pathological changes in the nerve. If left untreated, this stage is followed by impairment of capillary circulation that leads to changes in capillary permeability and leakage of protein into the tissues. This leads to accumulation of the proteinaceous fluid in the endoneural spaces which interferes with both the nutrition and metabolism of the nerve fibers. If the pressure continues, the previously described changes become permanent. The exudate serves as a matrix to fibroblast proliferation and the resulting intrafunicular fibrosis becomes irreversible. In the final stages, the nutrient vessel also becomes obliterated and the funiculi are replaced with what is essentially a fibrous chord. These pathological observations provide a strong rationale for early aggressive surgical treatment of the carpal tunnel syndrome. The clinical counterpart of the early stages, which fully are reversible, is the occurrence of pain and/or paresthesias, which most likely are due to a random discharge from hyperexcitable axons. The appearance of subjective numbness followed by objective numbness is a sign of total suppression of the transmission along the sensory pathways and probably corresponds to Stage II according to Sutherland. The appearance of a marked muscle atrophy is an ominous sign that, together with a longstanding objective sensory loss, probably indicates Sutherland's Stage III, which is irreversible. The resulting impairment in hand function and the loss of sensation of the three most important fingers of the hand are devastating, albeit preventable. Our experience indicates that the surgical release of the median nerve at the carpal tunnel can be done safely and effectively under local anesthesia in all patients, including the very old. The risks of surgery are negligible and the post-operative morbidity is minimal. Once a diagnosis of carpal tunnel syndrome is made we recommend that surgery under local anesthesia be performed within a few weeks, if rest and steroid administration are not effective. The waiting period eliminates the group of patients suffering from an "acute" carpal tunnel syndrome which usually is the result of strenuous, unaccustomed exercises of the hand, swelling of the flexor tendon sheaths, and a secondary median nerve compression. Similarly, a period of nonsurgical treatment should be tried if this syndrome occurs during pregnancy since it may subside spontaneously after delivery. If the symptoms, particularly the pain and paresthesias, become bothersome, the release of the median nerve should be performed early since this procedure can be performed safely during pregnancy as well.
Early surgery will eliminate not only the totally unnecessary suffering for the patient but also will prevent the development of irreversible changes in the nerve structures which are not amenable to any treatment modality once they are established.
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The surgical techniques have undergone significant improvement in recent years. In addition to routine use of the surgical microscope, high performance power drills permit more extensive removal of bone, which provides better exposure and minimizes the manipulation of neural structures. The use of specialized pin head holders allows precise positioning of the head based on the detailed preoperative diagnostic studies. Intraoperatively, the newest generation of bipolar coagulators allows pinpoint coagulation of the bleeding vessels. The resection of certain types of tumor is markedly facilitated by their aspiration after emulsification by an ultrasound instrument. This allows removal of even very large and firm tumors without undue traction on the surrounding structures which has been one of the main sources of mortality and morbidity in the past. New anesthetic techniques also have contributed to successful surgical results. The Swan-Ganz catheter placement preoperatively with computerized evaluation of cardiac function and intraoperative monitoring of cardiac output have been helpful particularly in elderly patients with depressed cardiac function who are subjected to intravenous fluid volume loading and cardio-depressant anesthetic agents during surgery. The results of the treatment of posterior fossa tumors have improved dramatically in the last ten years. For patients in whom tumor attachment to vital structures prevented complete removal, which was quite rare, the residual tumor is treated with post op radiations. The introduction of Gamma or Linac knife has been a major advance in treatment. Its effectiveness is markedly increased by significant "debulking" of the tumor mass which lessens the tumor load.
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