An unusual presentation of low ulnar nerve palsy: a case report

INTRODUCTION

The most common site of the ulnar nerve compression is at elbow in the region of cubital tunnel and less commonly at the wrist in the Guyon’s canal. At the level of the wrist, the nerve travel superficial to the flexor retinaculum and enter the hand through the Guyon’s canal and divide into superficial and deep branches. The site of nerve compression influences the symptoms. The nerve compressed proximal to the bifurcation yields both motor and sensory symptoms; compression along the deep motor branch produces pure motor symptom and the compression along the superficial branch produces pure sensory changes.

There are number of causes for ulnar nerve compression in Guyon’s canal such as acute trauma, hamate hook non-union, anomalous muscle, or space occupying lesion like ganglion, thrombosis and pseudoaneurysms. Ganglion itself is a very rare cause of ulnar nerve compression in Guyon’s canal.¹

CASE REPORT

A 65 years old man presented with the chief complaint of acute onset of weakness in right hand, feeling of numbness and heaviness in little finger and nocturnal pain over ulnar volar aspect of wrist within one and half months following the event of performing the strenuous exercise. Other associated complaints were bilateral knee pain. Patient was taking drugs for hypertension and benign prostate hypertrophy.

On examination

Right elbow

There was full range of motion. There was no palpable swelling. Mild tenderness was present below the medial epicondyle. There was wasting of interossei muscles and clawing of the little and ring finger.

Motor examination

Flexor carpi ulnaris = 4/5

Flexor digitorum profundo’s of little finger = 4/5

Hypothenar muscles = 0/5

Adductor pollicis brevis = 0/5

Flexor pollicis brevis = 0/5

Abductor pollicis brevis = 4/5

First dorsal interossei = 0/5

Sensory examination

Hypoesthesia was present along little and ring finger. Pin prick sensation was present. Two points discrimination was decreased. The patient couldn’t appreciate upto 14 mm. Ulnar nerve was tender at the wrist.

An X-ray was done which was normal. An ultrasound of right ulnar nerve was done. It reported that a well-defined cystic lesion was seen in the Guyon canal appearing to arise from pisotriquetral joint causing compression over the ulnar nerve. The size of the cystic lesion was 16x8 mm. Ulnar nerve appeared to be normal along its course in arm and forearm.

The Guyon’s canal was surgically explored. The neurovascular bundle was retracted. The ulnar nerve was carefully released through the Guyon’s canal. A ganglion measuring about 18x10 mm was excised. The incision was closed and a bulky dressing was applied.

At two weeks follow up suture were removed and the wound healed well. There was an improvement in sensation and the clawing persisted. At 5 months follow up time no clawing was present. There was no sensory deficit present and there was full motor recovery.

DISCUSSION

Guyon’s canal is a narrow anatomical space at the wrist through which passes the distal portion of the ulnar nerve. Its roof is formed by the volar carpal ligament and its floor by the transverse carpal ligament. Its ulnar boundary is formed by pisiform, pisohamate ligament and abductor digitiminimi. Its radial boundary is formed by the hook of hamate.² The canal is about 4 cm in length. The ulnar nerve divides into superficial sensory and deep motor branches as it passes though the canal. The course of ulnar nerve in Guyon’s canal is divided into three zones and compression at each zone produces unique set of symptoms. Zone 1 is proximal to the nerve bifurcation into superficial and deep branch. Compression in this zone produces both mixed motor and sensory symptoms. Zone 2 is present distal to the bifurcation and any lesion in this zone compresses the deep motor branch of the nerve and produces motor symptoms. Lesion in zone 3 compresses the superficial sensory nerve hence producing sensory symptoms only.³

Injury to the distal ulnar nerve can be caused by ganglion cyst, hook of hamate fracture, tumors like lipoma, repetitive injury, aberrant muscle e.g., abductor digitiminimi and ulnar artery thrombosis or aneurysm (hypothenar hammer syndrome).^4,5

The ulnar nerve compression in Guyon’s canal can often be confused with compression of the at the cubital tunnel. To distinguish between the two, the sensation over the dorsal ulnar aspect of the hand is checked. The dorsal ulnar cutaneous nerve provides sensation to this region and it does not pass through the Guyon’s canal and thus sensation will be preserved in case of ulnar nerve lesion in Guyon’s canal.⁶

Ganglion cysts account for 30% to 45% of Guyon syndrome cases.⁷ According to Kwak, ganglion cyst should be considered the most possible cause of ulnar nerve compression in sudden onset symptom.⁸

CONCLUSION

A thorough history and physical examination helps in making the diagnosis. Ultrasound is a cheap and non-invasive method of localizing the lesion along the ulnar nerve. Treatment is usually surgical with decompression of the ulnar nerve inside the canal and carefully excise the ganglion. Removal of the lesion helps in rapid recovery of the patient and attaining good hand function.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

REFERENCES

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