The diagnosis of the ulnar nerve lesion at Guyon's canal could be challenging. The characteristic sensory loss at the ulnar portion of the hand and weakness of all ulnar intrinsic hand muscles occurs when both the superficial and deep branches are affected.[ 7 , 10 ]
When only the terminal superficial or deep branches are affected, both due to intrinsic or extrinsic causes, uncommon clinical features could be seen. These unusual clinical presentations can be difficult to be interpreted by nonspecialists. Misdiagnosis can lead to equivocal treatment, delaying or preclude nerve recovery.
Case 1
A 55-year-old female presented to our outpatient facility complaining about 4 weeks history of weakness and clumsiness of the left hand without pain or sensory loss. She spontaneously denied any unusual situation but, after a thorough anamnesis, she remembered some light exercises, including a short bike ride on a weekend trip. Her medical records are unremarkable. Physical examination showed marked weakness and atrophy of all ulnar supplied intrinsic left hand muscles, except for the hypothenar muscles [ Figure 1 ]. No cutaneous sensory deficit and nerve tenderness (Tinel's sign) over Guyon's canal were present.
Figure 1:
Dorsal view of left hand. Note interosseous muscles atrophy, specially seen between I and II metacarpal bones (white arrow).
Before our evaluation, magnetic resonance imaging (MRI) of the cervical spine was performed showing no cervical myelopathy or compression of cervical roots and an electroneurography (ENMG), done just after initial symptoms, showed an unspecific axonal multineuropathy without motor conduction block. With these examinations, a suspected diagnosis of amyotrophic lateral sclerosis was performed by general physician and patient was sent to our institution. After our evaluation, a forelimb MRI was performed and no nerve compression was observed. The patient was submitted to another ENMG that confirmed ulnar neuropathy.
A surgical exploration was indicated after clinical complementary evaluation confirmed ulnar neuropathy. The procedure revealed a mild compression of the deep ulnar branch under the origin of the flexor digiti quinti brevis and opponens digiti quinti muscles [ Figure 2 ].
Figure 2:
Surgical view showing the pisohamate hiatus. The fibrous arch (white arrow) must be divided to release the deep branch of ulnar nerve. Note the deep branch of ulnar nerve (red arrow) passing posterior to the fibrous arch and the superficial branch of ulnar nerve (black arrow) passing anterior to the arch.
During the outpatient follow-up, the patient had an uneventful recovery with motor and sensory improvement.
Case 2
A 45-year-old female complained about weakness of the left hand with local pain and sensory loss in the IV, V fingers and hypothenar volar region in the 4th day of a 500 km road cycling amateur competition. After the end of the competition, the pain has gone but the rest of the symptoms remained. The patient presented to our outpatient facility 3 weeks after the end of cycling event. Her medical records were unremarkable.
Physical examination revealed mild weakness (Grade IV) and atrophy of all ulnar supplied intrinsic left hand muscles, including the hypothenar muscles, and hypoesthesia in the V finger [ Figure 3 ]. The nerve tenderness (Tinel's sign) over Guyon's canal was not present.
Figure 3:
Physical examination of hands. (a) Ventral view of hands, atrophy of ulnar innerved intrinsic hand muscles. (b) Close aspect of hypothenar region. Note left hypothenar region atrophy (white arrow).
A forearm and wrist MRI were requested and she denied being submitted an electroneuromyography. The MRI did not reveal any anomalies except the amyotrophy related. A conservative treatment was done with a good recovery.
The handlebar is one of the three contact areas that support the cyclist, beyond pedals, and the seat. Continuous and hyperextended position of the hand could compress and stretch both ulnar and median nerves at the wrist.[ 4 ]
The Guyon's canal lesions are usually divided into four places with distinct clinical aspects. Cavallo et al. proposed a clinical classification to distal ulnar neuropathy that can be easily applied to clinical practice.[ 3 ] The most common is the lesion proximal to the Guyon's canal (Type 1) characterized by sensory loss at the ulnar portion of the hand and weakness of all ulnar intrinsic hand muscles, last alteration being the most seen clinical aspect of it. More distal lesions inside the Guyon's canal (Type 2) cause an isolated palsy of the deep terminal motor branch without sensory loss. This lesion could be differentiated from Type 3 because the latter spares the hypothenar muscles. Type 4 affects the superficial branch only leading to sensory loss.[ 3 ]
The most reported etiologies of these lesions are the compressive in nature: lipoma, cysts, anomalies of ligaments or muscles, hook of the hamate fracture, and ulnar artery aneurysms. Extrinsic causes, such as chronic repetitive trauma or chronic pressure together with vibration, are not commonly reported, except if applied for months or years.[ 8 ] The most common sports associated with injuries of the ulnar nerve at the wrist is cycling.[ 9 ] Weightlift, rowing, gymnastics, and table tennis are more related to lesions of ulnar nerve at the elbow.[ 9 ] Wheelchair sports could affect both sites.[ 9 ]
The prevalence of ulnar and median nerve compression in long-distance cyclists ranges from 1 0% to 70%[ 5 ] with its characteristics motor or sensory disturbances. When no sensory involvement or pain is triggered by the sport, the cyclist can prolongate the activity without any change in the hand's position, leading to lesion progression.
When history is unclear and the clinical findings are not specific, further diagnostic workups are needed. ENMG and an MRI of the hand should be performed for the exclusion of pathological structures at Guyon's canal. Important differential diagnosis should be discarded, including radiculopathy of C8 and/or T1 roots. In pure motor syndromes, amyotrophic lateral sclerosis, multifocal motor neuropathy, and hereditary neuropathy with liability to pressure palsy (HNPP) should be ruled out.[ 2 ]
In our first case, the initial diagnosis caused intense stress and great suffering to the patient and her family. Her short history of cycling was an unusual cause of distal ulnar neuropathy, usually related to long-distance and repetitive cycling. Since the first report by Simpson[ 7 ] in 1895, literature reports describe cases of long-distance or prolonged cycling as possible extrinsic etiology for ulnar neuropathy. Few reports of ulnar neuropathy following short-distance cycling can be found, as Capitani and Beer[ 1 ] described in 2002, three cases of handlebar syndrome, one case of them was an unexperienced mountain biker that developed ulnar neuropathy after only one downhill mountain bike trip. Authors theorized the ri der posture, leaning too forward and an inadequate frame or handlebar grip as facilitating factors to rapid developing symptoms presented in that patient.
Although handlebar syndrome tends to recover with conservative management, it has to be early diagnosed to avoid a worsening of the case, as presented by the second patient. There is a lack of evidence-based recommendations on literature regarding handlebar syndrome treatment.[ 1 ] Most authors use Delphi consensus strategy recommendations derived from European HANDGUIDE study to guide their treatment. For mild-to-moderate symptoms, recommendations start with avoidance of local pressure and/ or limit mechanical overload including repetitive or static movements of the wrist and splinting the wrist in a neutral position in a fingers free splint for 1–12 weeks at night.[ 6 ] Surgery is reserved to patients with chronic symptoms or a severe presentation and consists of ulnar nerve exploration in the canal.[ 6 ]
Handlebar syndrome is a distal ulnar neuropathy cause by extrinsic repetitive compression of ulnar nerve at wrist. Its differential diagnosis can be challenging and must be ruled out before definitive diagnosis.
The incidence of handlebar syndrome should increase more and more with the increasing popularity of cycling sports, including mountain bike or long-distance cycling, so clinicians must be aware of this diagnosis. Surgical treatment is reserved to conservative management failure or anatomical anomaly found after imaging evaluation.
