A Proposal for the Definition of Hirayama Disease and Monomelic Amyotrophy

Update on the Pathogenesis, Clinical Diagnosis, and Treatment of Hirayama Disease

“…We classified these into six distinct types to better understand them. First, some names containing "distal, " for instance, juvenile muscular atrophy of (a) distal upper extremity, benign juvenile muscular atrophy of the distal upper extremity, distal bimelic amyotrophy, juvenile amyotrophy of the distal upper extremity, and segmental muscular atrophy of distal upper extremity with juvenile onset, are incomplete descriptions due to the presence of proximal alone or combined distal atrophy in a great number of cases; the use of such names will mislead clinicians, likely leading to misdiagnosis or delays in diagnosis (1,(9)(10)(11)(12). Second, monomelic amyotrophy (MMA) is a broader concept that includes crural MMA and brachial MMA; the latter includes other diseases that are characterized by atrophy of the upper limbs (13).…”

“…Second, monomelic amyotrophy (MMA) is a broader concept that includes crural MMA and brachial MMA; the latter includes other diseases that are characterized by atrophy of the upper limbs (13). It could be more appropriate to use the name "MMA" for similar cases that do not meet the characteristics and pathogenesis of HD and do not display other precisely defined disorders (10). Third, another term, benign focal amyotrophy, similar to MMA, involves either proximal or distal portions of the upper or lower extremities, with no compressive or traumatic etiology and arising later in life.…”

“…focal amyotrophy encompasses a more heterogeneous group of amyotrophies (14). Fourth, some names that include the term "spinal muscular atrophy" (SMA), for example, benign juvenile brachial SMA, distal SMA, and juvenile asymmetric segmental SMA, are not appropriate, for the reason discussed above (9)(10)(11). Fifth, cervical flexion (induced) myelopathy might be a suitable name for the entity, but it has been used relatively rarely in studies (15).…”

“…We recommend that the condition continue to be designated "Hirayama disease, " or juvenile benign muscular atrophy of upper extremity, according to current knowledge of the entity. Because, as adapted from the statements of Haluk Yavuz et al, HD is a type of juvenile muscular atrophy of the upper extremity with proximal, distal, and proximodistal involvement due to radiologically proven and arrested flexion myelopathy without sensory disturbance or with minimal sensory disturbance (10). From the perspective of pathogenesis that cervical flexion plays an important part in, it may be also called as juvenile cervical flexion myelopathy properly.…”

The Quantitative Assessment of Imaging Features for the Study of Hirayama Disease Progression

“…A large case report has confirmed that, after cervical spinal cord flexion, the probability of the appearance of forward displacement of the spinal cord and an abnormal signal image posterior to the dural sac in HD patients is approximately 87–95% [ 5 , 7 ]. Some scholars have even considered that because the pathogenic mechanism of HD remains unclear, only patients with the above specific image changes can be called “HD,” and others should be classified as the flexion type cervical spondylosis or unilateral muscular atrophy of the upper extremity [ 14 ]. Therefore, these authors have proposed that the probability of the presence of abnormal images in HD patients should be 100%.…”