Hirayama – bilaterality is a possibility!

A 20-year-old male patient with complaints of progressive weakness and difficulty in using both hands over a period of 6 months from difficulty in holding things and mixing foods to loss of muscle bulk in both hands and forearms (Fig. 1a, 1b - bilateral symmetrical distal forearm and hand muscle wasting with loss of thenar and hypothenar prominence). No loss of sensation or movement restriction at the shoulder joint. No history of neck pain, trauma or preceding fever.

Sagittal MRI T2WI image revealed asymmetrical focal cervical cord flattening in the lower cervical region (C5 – C7 vertebral level) (Fig. 2). On flexion MRI, T2WI sagittal image shows anterior displacement of the spinal cord with compression (Fig. 3). Loss of attachment (LOA sign) of posterior dura with subjacent lamina and anterior shift of the posterior dura (Fig. 4). T2WI and STIR hyperintense collection in the epidural space (Fig. 5, 6) extending from C3 to T8 vertebral level (max. thickness 8 mm) which shows strong homogeneous post contrast enhancement in Fat Sat T1WI sagittal image (Fig. 7a, b). Features are consistent with Hirayama disease.  Prominent epidural flow voids representing epidural venous engorgement are seen on sagittal T2WI (Fig. 8).

Electromyography findings:

Large Motor Unit Action Potential (MUAP), decreased cyclic adenosine monophosphate (cAMP) amplitude and discrete interference pattern with no elicitable response in right median and bilateral ulnar nerves. 

Hirayama et al [1] recognized in 1959 a disease characterised by insidious onset, asymmetrical weakness and wasting of distal muscles of the upper limb, affecting predominantly C7, C8, and T1 myotomes with male preponderance between 15 and 25 years of age. To describe this condition, the term "juvenile muscular atrophy of a unilateral upper extremity" was proposed. Other authors termed it “juvenile muscular atrophy of the distal upper extremity, juvenile asymmetric segmental spinal muscular atrophy, benign focal amyotrophy or monomelic amyotrophy” [2]. Hirayama disease is a benign disorder with a stationary stage after a progressive course (1-3 years). The most widely accepted hypothesis is a cervical myelopathy associated with neck flexion, proposed by Kikuchi et al [3]. Pathophysiology behind Hirayama disease is that loosely attached spinal dura mater is relatively short and tight and is unable to compensate for the increased length of the vertebral canal during neck flexion leading to LOA sign in axial MRI images. This results in tightening of the dural canal during neck flexion, which leads to an anterior shift of the posterior dural wall, causing spinal cord compression against the vertebral body leading to asymmetric lower cervical cord thinning which are usually diagnostic in MRI [4, 5]. Tashiro et al [3] recently outlined the criteria requirements for diagnosis of HD:

(1) Distal predominant muscle weakness and atrophy in forearm and hand

(2) Involvement of the unilateral upper extremity almost always

(3) Onset between the ages of 10 to early 20s

(4) Insidious onset with gradual progression for the first several years, followed by stabilisation

(5) No lower extremity involvement

(6) No sensory disturbance and tendon reflex abnormalities

(7) Exclusion of other diseases (e.g., motor neuron disease, multifocal motor neuropathy, brachial plexopathy, spinal cord tumours, syringomyelia, cervical vertebral abnormalities, anterior interosseous, or deep ulnar neuropathy)

In our case, there is bilateral symmetrical involvement with wasting of hand and forearm muscles with sparing of the proximal muscle group. There is obvious focal cord atrophy with flattening evident on MRI. Added to that, LOA sign with anterior shift of the dura and epidural collection which shows intense enhancement on flexion MRI and normal brain screening making Hirayama the only diagnosis for this atypical bilateral presentation. Though bilaterality rules out the possibility of monomelic amyotrophy (Hirayama disease) in the first instance, MRI added with flexion protocol helped us in narrowing this distinct diagnosis from brachial diplegia [6, 7].

Early diagnosis and therapeutic intervention in the form of cervical collar therapy minimises functional disability and helps in premature arrest of disease progression.

Written informed patient consent for publication has been obtained.