Introduction

Dystonia is one of the most common movement disorders and is characterized by intermittent or sustained muscle contractions that cause twisting, repetitive movements, or abnormal postures [1]. While dystonia is usually attributed to dysfunction in the extrapyramidal system, rare spinal cord lesions and peripheral nerve injuries have also been described in association with dystonia, although the pathomechanisms are poorly understood [2-4]. Herein, we report the case of a patient with focal hand dystonia due to hemorrhage of a cervical spinal mass and discuss this scenario in light of pertinent literature.

Case

Ethics statement: The authors certify that they have obtained all appropriate patient consent forms, in which the patient has provided consent for images and other clinical information to be reported in the journal.

Two months prior to presentation, a 65-year-old female patient was admitted to the emergency department with complaints of right upper extremity weakness, numbness, and pain radiating from the neck for 2 days. She also had an abnormal posture in the right hand which started 1 day after the onset of the other complaints. Cervical spinal magnetic resonance imaging was performed, and a space-occupying lesion in the right posterolateral epidural space was detected in the C4-T1 segments (Fig. 1A–1G). Subsequently, the patient underwent surgery and the mass was completely excised (Fig. 1H). After the surgery, her neck pain decreased from 10 to 7 on the Numeric Rating Scale (NRS); however, she still had weakness in the right upper extremity and abnormal posture of the right hand. Histopathological analysis of the excised tissue revealed a hematoma rich in fibrin and inflammatory cells. Electrodiagnostic tests revealed C7, C8, and T1 radiculopathy.

Two months later, the patient was referred to our outpatient clinic because of the aforementioned complaints. She denied any weakness, pain, or numbness in the other extremities, or any bowel or bladder incontinence. Her medical history revealed fibromyalgia and a mitral valve replacement 10 years prior, with ongoing anticoagulant therapy (warfarin, 5 mg/day).

Physical examination revealed restricted cervical spine movements. The right upper limb strength was as follows: shoulder abduction 4/5, elbow flexion 4/5, elbow extension 2+/5, wrist flexion 4/5, wrist extension 2+/5, and grip strength 3/5. Pinprick and light touch were decreased in the right C6-T1 dermatomes. Joint position and vibration senses were also lost in the 3rd, 4th, and 5th digits. Deep tendon reflexes were normal, except for right triceps hyporeflexia. She had a dystonic right-hand posture characterized by adduction and flexion of the 3rd, 4th, and 5th metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints (Fig. 2A). Neurological examinations of the left upper limb and both lower limbs were normal. The Babinski and Hoffmann signs were negative bilaterally.

Botulinum toxin A (BoNT) injections were performed under ultrasound guidance using a 5–12 MHz (Logiq P5; GE HealthCare, Chicago, IL, USA) linear probe. An out-of-plane technique was used, with an approach from the volar aspect of the hand when performing the injections. The BoNT injections were administered into the 2nd, 3rd, and 4th lumbrical muscles (15 IU each); 1st, 2nd, and 3rd palmar interosseous muscles (20 IU each); flexor digiti minimi brevis (10 IU); and opponens digiti minimi muscle (10 IU) of the right hand. Two weeks after injections, partial improvement in hand posture was observed (Fig. 2B, Table 1). The patient also underwent a 6-week (30-session) rehabilitation program that included cold application; occupational therapy; sensory reeducation; and range of motion, strength, and stretching exercises. Pregabalin 300 mg/day was administered to treat neuropathic pain. Eventually, her pain score decreased from 7 to 4 on the NRS, strength increased, and functional capacity improved. Physical examination results of the right upper limb before and after treatment are shown in Table 1.

Discussion

The site and nature of the pathologic mechanisms underlying the focal hand dystonia in this case are not clear. The localization could be spinal and/or peripheral (roots). Similar pathophysiological mechanisms have been suggested for both sites of involvement.

Spinal dystonia is an under-recognized phenomenon in spinal cord disorders, and compression and demyelination have been reported as the underlying causes [1]. Spinal dystonia can be fixed or paroxysmal and focal, segmental, or generalized [1]. Spinal pathologies may lead to abnormal sensory input, altered processing at spinal interneuronal circuits, or a primary disorder of the spinal motoneurons. Reflex inhibition of motor neurons by polysynaptic pathways in the spinal gray matter (interneurons) is modulated by descending pathways, allowing coordinated contraction of the limb musculature [2]. In our case, due to the compressive effect of the mass on the posterolateral side of the spinal canal, altered function of the spinal gray matter, possibly initiated by aberrant sensory stimuli, may have caused dystonic hand posture. Moreover, supraspinal mechanisms imply that erroneous sensory input from the spinal cord results in improper processing, and hence, aberrant motor output. Central sensory inputs are thought to play an important role in the development of dystonia [2,5].

However, peripherally induced dystonia remains controversial. Different types of peripheral injuries, with or without peripheral nerve lesions, may lead to focal dystonia at the site of injury [3,4]. Dystonia can occur within days or months (up to 1 year) after an injury [4,6]. Unlike action dystonia seen in primary (idiopathic) dystonia, peripherally induced forms are often characterized by a fixed posture [6]. Although the peripheral mechanisms of dystonia are not fully understood, its pathophysiology is explained by a decrease in ipsilateral reciprocal inhibition due to interneuronal dysfunction responsible for inhibition at the spinal level, which is regulated by cortical control and peripheral input from Ia afferent fibers [3,7]. In this regard, peripheral lesions may lead to focal dystonia by altering sensory input. Furthermore, various sensory abnormalities have been identified in patients, especially patients with focal hand dystonia, in whom increased thresholds of thermal detection and mechanical pain with decreased mechanical pain sensitivity on the affected extremity exist [8]. This suggests that dystonic hand posture can be attributed to loss of sensory function and impaired integration of proprioceptive input [8,9].

Individual predisposition and central reorganization in response to peripheral injury have also been found to contribute to the pathogenesis of peripherally induced dystonia [4,5,7]. The basal ganglia, cerebellum, thalamus, and their connections, coupled with altered sensory input, appear to play key roles in abnormal sensorimotor integration. Notably, central plasticity in response to altered peripheral input may result in maladaptive changes other than focal dystonia, such as neuropathic pain, which also occurred in our case [4].

Another important issue regarding focal hand dystonia is the treatment. However, management of this movement disorder is mostly symptomatic, as its neurological pathomechanisms are poorly understood. The most effective treatment for focal dystonia is local injection of BoNT targeting the affected muscles [10]. BoNT not only relaxes abnormally contracting muscles but also alters peripheral input by weakening intrafusal muscle fibers, leading to reduced spindle afferent activity [11]. In addition, ultrasound-guided injections of botulinum toxin into the intrinsic muscles of the hand play a pivotal role in the modulation of neuropathic pain. Indeed, botulinum toxin impedes peripheral sensitization and diminishes afferent C-fiber activity by preventing the release of acetylcholine at the motor endplates as well as calcitonin gene-related peptide and other nociceptive peptides at C-fiber nociceptor terminals, finally decreasing central sensitization [12].

The first step in BoNT treatment of hand dystonia involves careful evaluation and selection of the muscles to be injected. In addition to clinical evaluation, electromyography is widely used for this purpose [10]; however, side effects (e.g., weakness of non-injected muscles) have been reported after such injections [10,13]. Hence, ultrasound is paramount to ensure correct needle placement during injections [14] and may also demonstrate dystonic contractions, as observed in our case (Supplementary Video 1). As the intrinsic hand muscles serve as flexors at the MCP level, their contraction is the main cause of the dystonic intrinsic plus posture [15]. In our case, because the patient had a dystonic hand with flexion of the 3rd, 4th, and 5th MCP, as well as dystonic contractions during imaging (Supplementary Video 1), we injected into the intrinsic hand muscles (Supplementary Video 2). Moreover, the 3rd, 4th, and 5th PIP joints were in flexion and the 5th finger was in opposition. Although we also injected the hypothenar region, we did not target the flexor digitorum superficialis (FDS) to not diminish grasping function.

It has been noted that cooling the affected limb can transiently improve writer’s cramp by reducing the peripheral sensory input [16]. Moreover, sensory training has been effective in patients with focal hand dystonia [17]. Because we performed these interventions in our case, the improvement in the patient’s symptoms supports the importance of peripheral mechanisms in the pathophysiology of dystonia. The lack of full improvement in hand posture may have been due to the administration of low doses of BoNT to prevent weakness. As the patient complained of a flexion posture at the PIP joints of the 2nd and 3rd fingers at the end of the 6th week, we also planned to target the FDS muscle in follow-up visits.

To the best of our knowledge, focal hand dystonia due to mass hemorrhage in the cervical spinal canal has not been reported in the literature. Presenting this rare case, we would like to draw attention to the possible pathophysiological mechanisms of dystonia that are yet to be fully elucidated.

Supplementary materials

Supplementary Video 1.

Axial ultrasound imaging of the volar hand reveals dystonic contractions of the 2nd lumbrical, 1st palmar, and 2nd palmar interosseous muscles.

Supplementary Video 2.

Axial ultrasound imaging of the volar hand shows an out-of-plane botulinum toxin A injection into the 2nd palmar interosseous muscle.

Article information

Conflicts of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Author contributions

Conceptualization: all authors; Investigation: PA, HS, HBA; Visualization: PA, RG, BK; Writing-original draft: PA; Writing-review & editing: BK, LÖ.

Fig. 1.

Magnetic resonance imaging of the cervical spine. (A–C) Sagittal and (F) axial T2-weighted images (T2WIs) show a hypointense heterogenous space-occupying lesion (arrows) causing compression and anterior displacement of the spinal cord (F, asterisk) in the right posterolateral epidural space. (D) Sagittal T1-weighted image (T1WI) depicts hyperintense areas (arrows) within the mass that may represent hemorrhage. Note the contrast enhancement within the mass on the (E) sagittal and (G) axial post-contrast T1WIs. (H) Postoperative sagittal T2WI demonstrates total resection of the lesion.

Fig. 2.

(A) Dystonic posture of the patient's hand, characterized by flexion of the 3rd, 4th, and 5th metacarpophalangeal and proximal interphalangeal joints. (B) After botulinum toxin A injection, the flexion posture is partially improved.

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References

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