Hirayama Disease-Atypical Presentation

A 36-year-old male patient presents to the clinician with neck pain & right upper limb weakness which has increased over the last few years. Neutral MRI reported as degenerative discs. EMG showed denervation patterns in multiple small muscles of the right hand localized to C5-T2 dermatomes, then a flexion MRI was performed.

On neutral MRI, degenerative disc disease is seen with myelomalacia changes with focal cord atrophy at C5/6 (Figure -1, 2). On flexion MRI, there is anterior shift of the posterior dura extending from C4 to D2 (Figure-3, 4). Maximum indentation was noted at the level of C5 on the right side (Figure-5). In addition, there was atrophy and thinning of the cervical cord at this level. Multiple flow voids were seen posterior to the dura on T2W images (Figure-3). On post contrast study, there is enhancement in the venous plexus posterior to the displaced dura (Figure-6). Findings representing Hirayama disease.

Hirayama disease was first reported by Hirayama and colleagues in 1959 in Japan. Since then multiple cases have been reported in the Indian subcontinent [1]. Hirayama disease usually involves young adults in the age group of 15 to 25 years with characteristic male predominance. Although the disease might have started in adolescence, the presenting age can range from 15- 41 years [2].
As flexion MRI is not performed on all cervical spine studies, identifying the abnormality on neutral position becomes more important. Several signs have been described in the literature regarding findings seen on neutral position, which should alert the radiologist to perform a flexion MRI. Loss of attachment (LOA) of the posterior dura to the lamina is described by many authors as the most accurate finding on neutral MRI [2]. Other findings include abnormal cervical curvature, focal localized cord atrophy, and non-compressive intramedullary T2W high signal representing myelomalacia [3]. Loss of attachment (LOA) was however not seen in this patient and is likely to go unnoticed to an untrained eye. Other findings like focal cord atrophy and loss of cervical lordosis and focal intramedullary T2W hyperintense signal was attributed to degenerative disc on the neutral examination.
Dynamic MRI is the only way to differentiate between these conditions when the clinical examination is inadequate or inconclusive. Our patient was given a cervical collar and was followed up every 6 months. There was no further progression of the symptoms after 2 follow-ups. Definitive treatment in the form of cervical decompression with fusion is reserved for non-responsive cases.
Strong clinical suspicion in a young male patient with disproportionate atrophy of the cord should alert the radiologist and alter the examination in favour of a flexion study.