A 28-year-old male patient presented with progressive weakness of both forearms and hands along with clawing of hands for past eight years. Right side was affected more than the left. There was no history of similar illness in the family. There was no past history of any prolonged illness in childhood. There was no history of sensory, pyramidal or bladder dysfunction. There was atrophy of muscles of both forearms and hands. Muscle power was normal in both upper limbs. Nerve conduction studies showed reduced amplitude in bilateral median and ulnar nerves. Tendon reflexes were normal. Magnetic resonance imaging (MRI) examination was performed in non-flexion and flexed position. Subsequently, diffusion tensor imaging (DTI) was performed in non-flexion, which very clearly showed the cord atrophy at C7–T1 level. (Figure 1) This cord atrophy was not appreciated on MRI flexion and non-flexion studies. The diagnosis of Hirayama disease (HD) was thus established on DTI.

Hirayama disease (HD) is a non-progressive, juvenile, spinal muscular atrophy of distal upper limbs and is a kind of cervical myelopathy related to flexion movements of the neck. Imbalance in growth of vertebrae and dura mater causes a loss of normal dural slack in extension. As a result of this, the tight dural canal causes compression of the spinal cord. [1] It is suggested that HD might be due to microvascular changes following chronic trauma to spinal cord during flexion and extension of the neck. [2] On non-flexion MRI studies, asymmetric cord atrophy especially at the lower cervical level is highly suggestive of HD. [3] Furthermore, the magnetization and diffusion MRI histograms of the cervical cord suggest that the cord damage in HD extends beyond that seen on routine MRI scans. [4] In our opinion, this atrophy of the spinal cord is best demonstrated on diffusion tensor imaging. This makes diffusion tensor imaging a valuable tool in diagnosing Hirayama disease without subjecting the patient to a flexion study of the cervical spine.

Diffusion tensor imaging is simple, fast and accurate method for diagnosing Hirayama diasease without subjecting the patient to flexion magnetic resonance imaging study.

1. Hirayama K. Non - progressive juvenile spinal muscular atrophy of the distal upper limb (Hirayama's disease). In: De Jong JMBV, ed. Handbook of Clinical Neurology. Amsterdam, the Netherlands: Elsevier 1999;15:107–20.    
2. Hirayama K, Tomonaga M, Kitano K, Yamada T, Kojima S, Arai K. Focal cervical poliopathy causing juvenile muscular atrophy of distal upper extremity: A pathological study. J Neurol Neurosurg Psychiatry 1987 Mar;50(3):285–90.   [CrossRef]   [Pubmed]    
3. Chen CJ, Chen CM, Wu CL, Ro LS, Chen ST, Lee TH. Hirayama disease: MR diagnosis. AJNR Am J Neuroradiol 1998 Feb;19(2):365–8.   [Pubmed]    
4. Gallo A, Rocca MA, Tortorella P, Ammendola A, Tedeschi G, Fillipi M. A multiparametric brain and cord MR imaging study of a patient with Hirayama Disease. AJNR Am J Neuroradiol 2006 Nov-Dec;27(10):2115–7.   [Pubmed]