Successful treatment of focal hand dystonia after cervical whiplash injury by thalamotomy.

Background: Posttraumatic focal hand dystonia after cervical whiplash injury is rare. Moreover, the treatment of peripheral posttraumatic dystonia is usually ineffective. Herein, we report a case of successful thalamotomy for a patient with focal hand dystonia after cervical whiplash injury. Case Description: A 39-year-old woman was hit from behind by a car; subsequently, she felt strange in the right hand and was diagnosed with whiplash injury. A month later, she developed a persistent abnormal posture of the right hand. Brain imaging showed no lesions, and cervical magnetic resonance imaging showed stenosis but no spinal cord signal changes. Posttraumatic dystonia was diagnosed, for which the patient underwent left ventro-oral (Vo) thalamotomy. One year after the first surgery, the patient underwent left Vo and ventral intermediate nucleus (Vim) thalamotomy due to recurrence of dystonia. Nine years after the second surgery, the patient continues to be able to maintain her normal physical routine.
Conclusion: Vo-Vim thalamotomy may be a feasible and effective treatment for focal hand dystonia after cervical whiplash injury. Copyright:

INTRODUCTION

Trauma is thought to be a cause of secondary dystonia.[5] Although controversial, peripheral trauma which is defined as trauma outside the central nervous system (CNS) can also be a cause of dystonia. Cervical whiplash injury is common, and some cases of posttraumatic dystonia following whiplash have been reported.[5,17] The most common form of dystonia following whiplash is cervical dystonia, while focal hand dystonia after whiplash is rare.[1,4,14,15] The report of surgical interventions of posttraumatic dystonia, especially peripheral posttraumatic dystonia, is very rare.[2,10] Ventro-oral (Vo) thalamotomy is one of the candidate treatments for primary focal hand dystonia.[8,13] However, no reports have revealed the outcome of Vo thalamotomy in a patient with peripheral posttraumatic focal hand dystonia. Herein, we report a case of successful Vo and ventral intermediate nucleus (Vim) thalamotomy for a patient with focal hand dystonia after cervical whiplash injury. We have also provided a review of the literature regarding posttraumatic dystonia.

CASE REPORT

The patient was a 39-year-old right-handed woman with an unremarkable medical history. She was hit from behind by a car while waiting at a traffic signal on her motorbike; subsequently, she had neck pain and felt restricted movement in the right hand. The patient was diagnosed with whiplash injury. One month later, she developed a persistent abnormal posture of the right hand. Electrophysiological examination showed no abnormal findings. Head computed tomography (CT) and brain magnetic resonance imaging (MRI) showed no lesions. Cervical MRI showed cervical canal stenosis but no spinal cord signal change. She was diagnosed with posttraumatic dystonia and referred to our hospital for surgical treatment.

On admission, her right thumb was adducted at the metacarpophalangeal (MP) joint and extended at the distal interphalangeal (DIP) joint. The second to fourth fingers were fixed in flexion at the DIP and proximal interphalangeal (PIP) joints. Her fifth finger was flexed at the DIP and PIP joints and extended at the MP joint [Figure 1]. She was able to voluntarily extend or flex her fingers a little, but when she attempted to grip, her wrist flexed involuntary. She reported no pain in her right hand. Although she reported some discomfort in her right lower limb, she was able to walk. Consequently, we planned Vo thalamotomy for focal hand dystonia after cervical whiplash injury.

Figure 1:

Improvement of the patient’s right hand posture over the course of thalamotomy. Writing posture (a) and posture while holding a cup (b) before the surgery. Writing posture after the surgery (c).

First surgery

The patient underwent left Vo thalamotomy with the stereotactic target set at 1 mm above, 15 mm lateral to, and 2 mm posterior to the midpoint of the anterior commissure/ posterior commissure line. Surgery was performed under local anesthesia without any microelectrode recording. A monopolar radiofrequency probe (tip diameter, 1.0 mm; uninsulated length, 4.0 mm) was used. Macrostimulation (130 Hz, 100 μs pulse width, up to 15 mA) did not induce any adverse effects. Coagulation was performed at 70°C for 30 s at the tentative target, after which the electrode was withdrawn.

The extension and flexion of the right finger became smooth during the operation. There were no neurological deficits including paresthesia, dysphagia, sensory loss, or motor paresis after the surgery.

One day after the surgery, the patient extended and flexed the second to fourth fingers. Wrist movement got smooth. Seven days after the operation, the patient could write smoothly and was discharged. The patient reported recurrence of the right hand dystonia 14 months later; accordingly, revision surgery was planned.

Second surgery

The patient underwent left Vo and Vim thalamotomy; the stereotactic target coordinates, anesthesia, radiofrequency probe used, and coagulation procedure were all the same as those used for the first surgery. Macrostimulation (130 Hz, 100 μs pulse width, up to 15 mA) did not induce any adverse effects. Coagulation was performed at the tentative target. The electrode was withdrawn in 1 and 3 mm increments to increase lesion size, resulting in three contiguous lesions. As symptoms did not improve, the target was changed to 3 mm anterior and 3 mm posterior to the previous target. Three contiguous lesions anterior and two lesions posterior to the tentative target were made, resulting in a total of eight lesions [Figure 2]. After coagulation, the movement of the patient’s right hand became smooth.

Figure 2:

Lesions revealed by T1-weighted MRI. A coagulation lesion can be seen on the ventro-oral (Vo) and ventral intermediate nucleus (Vim) border of the left thalamus before the second surgery (a and b). After the second surgery, coagulation lesions can be seen on both the Vo and Vim of the left thalamus (c and d).

There were no neurological deficits including paresthesia, dysphagia, sensory loss, or motor paresis after the second surgery. The patient was discharged 7 days after the second surgery. At the 8-year follow-up, although she reported occasionally experiencing awkwardness in her right hand, especially on cold days, the patient has maintained her normal physical routine.

DISCUSSION

Although trauma often precedes the onset of dystonia, its role in the development of dystonia has medical, psychological, and legal implications and is a controversial topic.[5] Posttraumatic dystonia can be classified into two types based on injury location. Central posttraumatic dystonia (CPD) usually occurs following severe head trauma; in such cases, onset can be delayed, confounding the association.[5] Lesions are commonly observed on brain MRI or head CT. Peripheral posttraumatic dystonia (PPD) refers to the rare occurrence of dystonia following trauma to a region of the body outside the CNS. Complex regional pain syndrome may occur concurrently with dystonia, although the trauma is generally less severe compared to that in CPD. The onset of PPD is generally within a few days to 1 year after the injury. In the present case, the trauma was a typical whiplash injury sustained when the patient was hit from behind by a car. The patient’s right hand was affected immediately after the injury, with abnormal posture developing and worsening within 1 month. The patient had no lesion of brain, cervical, or limbs lesions at the accident. Most cases of posttraumatic dystonia after cervical whiplash injury involve torticollis or cervical dystonia.[4,15] Posttraumatic focal hand dystonia after a cervical whiplash injury is rare.[1,14] Regarding whether posttraumatic dystonia after cervical whiplash injury should be classified as CPD or PPD, Tamburin and Zanette reported the case of a patient who developed a dystonic posture after a cervical whiplash injury caused by a small lesion on the cervical spinal cord.[14] As the cervical spinal cord is part of the CNS, it was a case of CPD. In contrast, whiplash induces pressure on the nerve root ganglia,[16] which are outside the CNS; therefore, if a nerve root is injured, posttraumatic dystonia after whiplash is PPD. In our case, there were no lesions in the brain or cervical cord, and the onset of symptoms occurred immediately after the injury. These findings imply that this was a case of PPD.

The treatment of PPD, most commonly using botulinum toxin injections,[3,18] is usually ineffective.[5,9,10] Vo thalamotomy is one of the candidate treatments for focal hand dystonia.[8,13] The Vo nucleus of the thalamus is a relay point in the corticobasal ganglia-thalamo-cortical circuit and a major termination site for basal ganglia outputs that control the motor cortex. The effects of Vo thalamotomy on focal hand dystonia may be based on alteration in this basal ganglia-thalamo-cortical circuit.[8] The effectiveness of Vim thalamotomy has also been previously reported.[11,12] Moreover, recurrence after Vo thalamotomy has been reported to occur due to insufficient or incorrect coagulation over the entire Vo nucleus of the thalamus.[7] In our case, the thalamotomy lesion after the first operation did not cover a part of the Vo nucleus [Figure 2]. Therefore, in the second surgery, the target should be more on the posterior side. As a result, Vim coagulation was added. The Vop-Vim may be a target for focal hand dystonia in the cases of failure of Vo thalamotomy.[6] After the second surgery, the lesions covered both the Vo and Vim. In fact, it is unclear which parts of Vo and Vim should be targeted; this aspect also needs further investigation. Due to symptom recurrence, the patient underwent rethalamotomy, which ultimately resulted in a successful outcome.

CONCLUSION

Here we presented a patient with focal hand dystonia after cervical whiplash injury. Vo-Vim thalamotomy may be a feasible and effective treatment for peripheral posttraumatic dystonia.