Monomelic amyotrophy (hirayama disease) with upper motor neuron signs: a case report.
Monomelic amyotrophy (MMA), also known as Hirayama disease, is a sporadic juvenile muscular atrophy in the distal upper extremities. This disorder rarely involves proximal upper extremities and presents minimal sensory symptoms with no upper motor neuron (UMN) signs. It is caused by anterior displacement of the posterior dural sac and compression of the cervical cord during neck flexion. An 18-year-old boy visited our clinic with a 5-year history of left upper extremity pain and slowly progressive weakness affecting the left shoulder. Atrophy was present in the left supraspinatus and infraspinatus. On neurological examination, positive UMN signs were evident in both upper and lower extremities. Electrodiagnostic study showed root lesion involving the fifth to seventh cervical segment of the cord with chronic and ongoing denervation in the fifth and sixth cervical segment innervated muscles. Cervical magnetic resonance imaging (MRI) showed asymmetric cord atrophy apparent in the left side and intramedullary high signal intensity along the fourth to sixth cervical vertebral levels. With neck flexion, cervical MRI revealed anterior displacement of posterior dural sac, which results in the cord compression of those segments. The mechanisms of myelopathy in our patient seem to be same as that of MMA. We report a MMA patient involving proximal limb with UMN signs in biomechanical concerns and discuss clinical importance of cervical MRI with neck flexion. The case highlights that clinical variation might cause misdiagnosis.
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Seung Don
SD
Yoo
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Hee-Sang
HS
Kim
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Dong Hwan
DH
Yun
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Dong Hwan
DH
Kim
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Jinmann
J
Chon
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Seung Ah
SA
Lee
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Sung Yong
SY
Lee
Department of Physical Medicine and Rehabilitation, Kyung Hee University School of Medicine, Seoul, Korea.
Yoo Jin
YJ
Han
Biological assays; Monomelic amyotrophy; Pyramidal signs