Hirayama disease: A case report

Abstract

Hirayama Disease is a spinal muscular atrophy which presents with varying degrees of unilateral or asymmetric bilateral distal muscle weakness of the upper extremity. It is a rare, non-progressive motor neuron disease, mostly affecting young males. Although considered to have a relatively stationary clinical course after a period of initial progression, it can be functionally impairing in some patients. Here, we present a case of a 20-year-old male who complained of weakness of his right upper extremity for 1 year with difficulty performing activities of daily life. This case highlights the role of radiologist in identifying the subtle findings in cervical spine MRI of patients with such presentation. Moreover, it emphasizes the importance of including flexion imaging MRI sequences in a patient with suspicion of Hirayama disease.

Background

Hirayama disease was first described by a Japanese neurologist Keizo Hirayama in 1959 [1]. It is also known as monomelic amyotrophy and juvenile muscular atrophy of unilateral upper extremity. It is a disease causing unilateral or asymmetric bilateral weakness and atrophy of distal muscles of upper extremity. Hirayama disease is considered to be a rare motor neuron disease with most cases reported from Asia, with varying prevalence reported such as 1 in 30000 in Japan [2] and 10-year prevalence of 5.54 in 100,000 in South Korea [2].

Case presentation

A 20-year-old male presented to the clinic with a 1-year history of progressive weakness of the right forearm and hand. The patient had first noticed gradual worsening of symptoms over the initial 5 months, characterized by difficulty in holding cups, riding a bicycle, and performing simple household tasks. The patient reported having no further progression of symptoms thereafter. There was no preceding trauma, nape pain, headache, blurring of vision, dizziness, gait imbalance or bowel and bladder dysfunction.

The patient gave no history of smoking, alcohol consumption or substance abuse. There was no history of any surgery or illnesses in the past. There was no history of similar symptoms in any of his family members. On physical examination, there was noticeable wasting of the distal flexor and extensor muscles, hypothenar as well as dorsal interossei muscles on right (Figs. 1A and B). Muscle weakness was noted upon wrist flexion and extension, digits abduction, adduction and thumb opposition. Likewise, the grip strength was reduced. A subtle, low-amplitude tremor was observed during finger extension, characteristic of minipolymyoclonus (Video clip 1). Reflexes were normal with no evident clonus. Sensory examination was normal. The proximal muscle groups had preserved power with no visible wasting and there were no abnormal findings in the lower limbs nor the contralateral upper limb. Blood tests including complete blood count, erythrocyte sedimentation rate, C-reactive protein were normal. Thyroid function test was within normal limits. Additionally, Vitamin D level, creatine kinase and alkaline phosphatase were also within normal parameters.

Fig. 1.

Images showing notable wasting of hypothenar muscles of the right extremity in a 20 year old male with Hirayama disease. Image B further shows wasting of the forearm muscles.

Plain and contrast enhanced MRI (magnetic resonance imaging) of cervical spine was performed with neutral neck position and flexion of the neck. There was slight thinning of the spinal cord at the level of C5-C7 without any signal abnormality (Fig. 2A). The corresponding axial scan showed asymmetry of the spinal cord with subtle posterior flattening towards the right (red arrow in Fig. 2B). During flexion, anterior displacement of the posterior thecal sac (Fig. 3B) was noted at C4-C7 vertebral levels compared to its position in the neutral image (Fig. 3A). Upon contrast administration, enhancement of the posterior epidural region was noted at this level (Fig. 3C). Additionally, incidental note of mild disc bulge at C3-C4, C4-C5, C5-C6 levels were noted without significant neural foraminal narrowing.

Fig. 2.

(A) Sagittal T2 weighted MRI of the cervical spine upon neck flexion shows slight atrophy of the spinal cord at C5-C7 levels (yellow box). There is mild compression of the spinal cord between the spinal column and posterior dura. (B) Corresponding T2 transverse image at C5-C6 level shows asymmetry of the spinal cord with subtle posterior flattening towards the right (red arrow).

Fig. 3.

Sagittal T1 images (A) on neutral neck position and (B) with neck flexion show anterior bulging of the posterior dural sac during flexion (between green bracket) (C) Enhancement of the posterior epidural region evident in the involved segments (C4-C7 levels) after contrast administration (yellow arrows).

The patient was subsequently diagnosed as Hirayama disease, started on physiotherapy and placed on cervical collar. He was reassured about the benign nature of the condition. He was first followed up after 1 month to assess compliance with treatment. He was regular with his physiotherapy and used cervical collar as advised. No significant change was noted in his symptom during this period. He has been advised for further regular follow up to monitor his symptoms and modify management strategies accordingly.

Discussion

Hirayama disease has been known to have a male preponderance [2] primarily in their adolescence and young adulthood. It is a non-hereditary and non-progressive condition [3]. However, some cases of familial association have been mentioned in the literature [4]. It has been hypothesized that the disproportional growth between the dura and the vertebra leads to taut dura, which is more noticeable upon flexion leading to loss of attachment of the posterior dura from the posterior lamina [2,5,6]. This growth discordance is accentuated during the adolescent growth spurt [7].

The loss of posterior dural sac attachment to the underlying lamina may restrict its elongation during neck flexion, displacing the cord anteriorly and compressing it against the posterior margin of the vertebral bodies. Chronic ischemic changes in the anterior spinal artery territory, primarily the anterior horn cells, then ensues [2] leading to localized cord atrophy, intramedullary ischemic change or gliosis [6]. This mostly occurs at the site of the most kyphotic level (usually C4 - C6). The forward shift of the dura leads to increased negative pressure in the epidural venous plexus and resultant congestion which is seen in MRI as increased epidural enhancement upon contrast administration [5,6].

Patients present with lower motor neuron type weakness and atrophy in the distal upper extremity muscles, with characteristic sparing of the brachioradialis [2]. No sensory loss is noted. The involvement is usually unilateral or asymmetric if bilateral. Even though the disease is believed to be stable after a certain initial stage of progression, it can cause significant functional limitation in some patients. In our patient, the symptoms were noted to worsen in the first 5 months and remained relatively constant after that. Besides the physical manifestation, patient was distraught emotionally due to his impaired ability to carry out his activities of daily living.

MRI findings [2,3,5,6,8]

Neutral and flexion imaging of cervical spine before and after contrast administration is usually suggested to diagnose Hirayama disease. Some of the MRI findings commonly described in the literature include loss of spine lordosis [6], cord atrophy and asymmetric posterior cord flattening at the involved segment, intramedullary high signal intensity in T2 weighted images (T2WI) corresponding to the area of the anterior horn cells, loss of attachment of the posterior dura from lamina in neutral spine image [5] exacerbated upon flexion, enhancement and hyperemia in the posterior epidural venous plexus due to congestion. In our patient, most of the described findings were noted. However, no intramedullary high signal intensity was noted in T2WI and loss of attachment of the posterior dura from lamina was not appreciated in neutral spine image.

The disease is usually self-limiting in a few years but residual deficits may remain. Complications including disuse atrophy and permanent contractures may occur [2]. Aim of treatment is focused mainly to decrease symptoms, improve function and prevent complications. Usually, conservative management is done with physiotherapy and cervical collar to limit the exacerbating neck movements until growth spurts are complete [2]. Surgical interventions of the spinal elements or the involved upper extremities have achieved good outcomes [2,9] in those who fail to respond to conservative management.

Differential diagnoses for upper extremity amyotrophy include cervical myelopathy due to spondylosis, spinal cord neoplasia, trauma, infection, syringomyelia and amyotrophic lateral sclerosis [7].

Conclusion

Hirayama disease could actually be more common but remain under recognized due to the high index of clinical suspicion required on the primary clinician’s as well as radiologist’s part. The subtle findings on imaging may easily be missed if the radiologist is not aware of this entity. Additionally, routine MRI protocol doesn’t include imaging the spine during flexion and the findings in the neutral spine sequences may remain undetected or even normal. Therefore, it is essential for all multidisciplinary team involved in patient care and diagnosis to be aware of this entity for early diagnosis and optimum management.

Patient consent

Written informed consent was obtained from the patient for the use of images and relevant clinical details in this case report. No patient identifiers have been included in this report.

Appendix. Supplementary materials

Video clip 1 demonstrating minipolymyoclonus