Thrombosis of the persistent median artery as a cause of carpal tunnel syndrome - case study.

Carpal tunnel syndrome is the most frequent neuropathy of the upper extremity, that mainly occurs in manual workers and individuals, whose wrist is overloaded by performing repetitive precise tasks. In the past it was common among of typists, seamstresses and mechanics, but nowadays it is often caused by long hours of computer keyboard use. The patient usually complains of pain, hypersensitivity and paresthesia of his hand and fingers in the median nerve distribution. The symptoms often increase at night. In further course of the disease atrophy of thenar muscles is observed. In the past the diagnosis was usually confirmed in nerve conduction studies. Nowadays a magnetic resonance scan or an ultrasound scan can be used to differentiate the cause of the symptoms. The carpal tunnel syndrome is usually caused by compression of the median nerve passing under the flexor retinaculum due to the presence of structures reducing carpal tunnel area, such as an effusion in the flexor tendons sheaths (due to overload or in the course of rheumatoid diseases), bony anomalies, muscle and tendon variants, ganglion cysts or tumors. In some cases diseases of upper extremity vessels including abnormalities of the persistent median artery may also result in carpal tunnel syndrome. We present a case of symptomatic carpal tunnel syndrome caused by thrombosis of the persistent median artery which was diagnosed in ultrasound examination. The ultrasound scan enabled for differential diagnosis and resulted in an immediate referral to clinician, who recommended instant commencement on anticoagulant treatment. The follow-up observation revealed nearly complete remission of clinical symptoms and partial recanalization of the persistent median artery.

Introduction

Carpal tunnel syndrome is the most frequent neuropathy of the upper extremity which can be caused by different factors. It mainly occurs in individuals whose wrist is overloaded during repetitive manual work. At present, it is most frequently caused by long hours of computer keyboard use. Previously, this median nerve neuropathy had been considered an occupational disease of typists, seamstresses and mechanics.

The patient usually complains of pain, hypersensitivity and paresthesia of his hand and fingers in the median nerve distribution. In further course of the disease atrophy of thenar muscles is observed. Nocturnal symptoms are very typical and usually wake a patient up, forcing him to move and wriggle his wrist and hand.

The direct cause of median nerve compression is an increased pressure within the carpal tunnel due to the presence of changes reducing carpal tunnel area, such as an effusion in the flexor tendons sheaths (due to overloading or in the course of rheumatoid diseases), bony anomalies within carpal tunnel, muscle variants (additional or low attached muscle belly) and flexor tendons variants, ganglion cysts and soft tissue tumors. Diseases of upper extremity vessels may be also a cause of carpal tunnel syndrome. This includes changes in a persistent median artery intercalated between the two parts of the median nerve.

Case report

A 39-year-old female patient was referred for an ultrasound scan, with a few days history of severe pain, weakness and numbness of her right wrist and hand. She worked as a cleaner and associated her symptoms with her work, they were aggravated by performing cleaning activities.

Her physical examination did not show any thenar muscles atrophy or skin changes including skin paleness, the skin temperature of her hand was normal and the pulse on radial artery was well palpable.

An ultrasound scan of the wrist was performed with a linear transducer 14 MHz. It did not reveal any effusion or synovial pathology within the joints, flexor and extensor tendon sheaths. The appearance of flexor and extensor tendons at wrist level was normal. A small ganglion cyst measuring 12×4 mm was detected between the navicular and trapezoid bone. The median nerve was in bifid form and a persistent median artery was seen between its two parts. The median artery at wrist level was not prone to probe compression whereas its proximal part at the forearm level was prone to probe compression. Power Doppler examination revealed a segment of arterial thrombosis measuring 2–3 cm (fig. 1). The total area of both parts of the median nerve was 13 mm2. The diameter of persistent median artery at the thrombosed fragment was 2.4 mm in comparison to the unaffected normal proximal segment – 1.2 mm. On the forearm, laterally to the median artery, a patent radial artery was seen with diameter of 2.4 mm (fig. 2).

Fig. 1

Persistent median artery at wrist level: A. B-mode image; B. in PD examination no-flow (black arrow), in ulnar artery flow visible (empty arrow)

Fig. 2

A. Radial artery (empty arrow), persistent median artery (black arrow) and their diameters at the level 2/3 distally of forearm. B. An image of persistent median artery with suggested places of probe positioning: 1 – level of pisiform bone, 2 – level of distal 2/3 of the forearm

On the basis of these sonographic findings the patient was urgently referred to a surgeon. The surgeon started her on anticoagulant therapy and referred her for further rheumatological evaluation to exclude rheumatoid diseases. During the diagnostic process, laboratory results were obtained (thrombocyte count, APTT, INR, D-dimer level) excluding both hemostatic disorders and antiphospholipid syndrome (the latter promotes thromboembolic state and our patient had a history of miscarriage at 13th week of pregnancy). She was also tested for lupus anticoagulant, B2 glycoprotein-I antibodies and anticardiolipin antibodies – all the results were normal. Neither antinuclear antibodies nor inflammatory markers were detected. Whilst giving medical history she did not complain of any arrhythmia disorders, denied any significant bacterial infection prior to the incidence of thrombosis. She did not have any other risk factors such as history of smoking, significant obesity, lipid disorders, diabetes, arterial hypertension or lack of physical activity.

During three months’ follow-up nearly complete remission of the clinical symptoms and partial but satisfying recanalization of the persistent median artery was observed (fig. 3).

Fig. 3

Follow-up scan after three months partial recanalization of median artery (black arrow)

Discussion

Thanks to technical development, ultrasound scan of the musculoskeletal system has become a standard procedure in the diagnostic algorithm of patients with musculoskeletal complaints, allowing for assessment of soft tissues: tendons, ligaments, muscles and nerves(. The technique of median nerve examination and its evaluation criteria, including the aspect of its possible pathologies, have been described in 49th issue of “Journal of Ultrasonography”(. One of the mentioned pathologies is an anatomical variant known as bifid median nerve. Lanz in studies conducted on cadavers found that anomaly in 2.8% of examined hands(. The detection of this anomaly, including the possibility of a persistent median artery presence between the parts of the nerve, is of vital importance before planned surgical intervention(. The presence of a persistent median artery, however, is not necessarily associated with any symptoms. The vessel is frequently present in people without complaints typical of carpal tunnel syndrome and this can be confirmed by sonographic examination. Gassner at al. confirmed the presence of a persistent median artery unilaterally in 20% healthy volunteers and bilateral anomaly was found in 6% healthy volunteers(.

A case similar to our patient's, with thrombosis of persistent median artery was presented by Fumière(. In both cases, the contralateral median nerve was normal and complaints at the affected site were aggravated by physical work(.

Conclusion

Ultrasound evaluation is the basic method of median nerve morphology assessment. Median nerve and its anatomical variants together with its pathologies can be also seen in MRI scan. However, due to the fact that the median nerve is easily accessible at wrist level, and that the ultrasound scan is simple and cost effective it is the method of choice( in a patient with symptoms typical for carpal tunnel syndrome (CTS). Ultrasound allows for differential diagnosis of numerous complaints characteristic of this entity. Secondly, it allows for planning of further diagnostic procedures (imaging or functional tests) and proper specialist referral. In the presented case, an ultrasound examination allowed us to make a immediate diagnosis of the thrombosed persistent median artery, a quick referral to a surgeon and commencement of anticoagulant therapy.