362 PRACTICAL NEUROLOGY Pract Neurol: first published as 10.1111/j.1474-7766.2004.00265.x on 1 December 2004. Downloaded from NEUROLOGICAL RARITIES Monomelic amyotro Hirayama’s dis INTRODUCTION HISTORY The patient presenting with weakness and The fi rst report of non-progressive amyotro- wasting of one limb, usually the arm, can be a phy of the upper limb appeared in 1959 when considerable diagnostic challenge for the neu- Hirayama desribed 12 patients (Hirayama et al. rologist. While the spectre of the amyotrophic 1959). Subsequently, as larger series of patients lateral sclerosis form of motor neuron disease were reported from Japan, a distinct clinical en- (ALS/MND) is often in the clinician’s mind, tity emerged (Hirayama et al. 1963; Sobue et al. there is also a signifi cant differential diagnosis 1978). Males accounted for over 80% of cases, to be considered. While this article discusses a typically with onset between 15 and 25 years of number of well-known conditions that should age. One of the most consistent features through be in the differential diagnosis, I will focus par- to the present day is the striking unilaterality in http://pn.bmj.com/ ticularly on a lesser known condition, Hiraya- the majority of cases, an observation that casts ma’s Disease (also known as Sobue Disease doubt on the plausibility of the spinal cord com- in North America), that is only rarely seen in pressive basis of the condition discussed below. European populations and may therefore be After initial reports it became apparent that the less familiar to neurologists outside Japan and condition was also found not infrequently in the on September 25, 2021 by guest. Protected copyright. India. Indian subcontinent (Gourie-Devi et al. 1984). Monomelic amyotrophy or ‘juvenile non- Then in recent decades a steady number of progressive amyotrophy of the upper limb’ is cases have been reported from Europe, though rarely encountered in the general neurology relatively few from the UK (de Visser et al. 1988; clinics but it may be under diagnosed. Previously Serratrice 1991). As the disorder became more thought to be restricted to Japan and South Asia, frequently recognized it is now apparent that it is now clear that this condition does occasion- onset can be in later life and with a higher fre- ally occur in Europe and merits consideration quency in women than hitherto appreciated in any patient presenting with pure lower motor (van den Berg-Vos et al. 2003). And as the de- neuron weakness of one upper limb. Further- bate about whether this condition represents a more the term ‘juvenile non-progressive amyo- focal form of primary lower motor neuron de- trophy’ coined by Hirayama is probably not ideal generation (i.e. a focal form of spinal muscular as it is clear that many cases do progress, albeit atrophy), or the local consequence of anatomi- extremely slowly. While not obviously treatable, cal variation in the cervical spine continues, the the chief benefi t in making the diagnosis is in terminology used has become if anything more allaying fears of a much more malignant neuro- confusing with Japanese authors now favouring logical disorder such as MND. the term ‘cervical polidystrophy’. © 2004 Blackwell Publishing Ltd DECEMBER 2004 363Pract Neurol: first published as 10.1111/j.1474-7766.2004.00265.x on 1 December 2004. Downloaded from ophy or Kevin Talbot Honorary Consultant Neurologist, Department of Clinical Neurology, Radcliffe Infi rmary, Oxford; E-mail: [email protected] sease Practical Neurology, 2004, 4, 362–365 CLINICAL PRESENTATION ments carry a self-fulfi lling circularity. Tendon In contrast to other lower motor neuron dis- refl exes can be reduced, normal or even exag- orders such as spinal muscular atrophy, mono- gerated. melic amyotrophy is essentially a sporadic, not The wasting and weakness characteristically a genetic condition. In all series reported from involves muscles innervated by the C7-T1 seg- Asia to date there has been a male preponder- ments. Thus the shoulder girdle is usually spared ance in a roughly 10 : 1 ratio. Although rare in and there is often a striking sparing of brachio- the West, monomelic amyotrophy accounted radialis (C5,6) in the forearm, giving rise to an for 13% of patients seen at a centre for motor appearance which Hirayama called ‘oblique neuron disorders in South India over a 10-year amyotrophy’. Fasciculations appear to be rare. In period (Gourie-Devi & Nalini 2003). the most extensive long-term follow up to date, http://pn.bmj.com/ The onset is insidious over months or years Gourie-Devi and Nalini showed that within a without any history of antecedent trauma or in- few years progression appears to arrest and pa- fection. The median age of onset in Asian case tients followed up for more than 20 years never series is in the early 20s but with a broad range go on to develop progression to other areas of extending from 15 to 35 years. However, in a the motor system. In addition to weakness and on September 25, 2021 by guest. Protected copyright. large Dutch retrospective series of lower motor wasting, patients have described worsening of neuron disorders, 16/49 patients had a condi- their symptoms in cold weather. tion with the same clinical features as Hiraya- ma’s monomelic amyotrophy, with an age of DIFFERENTIAL DIAGNOSIS OF THE WEAK onset ranging from 18 to 65 and with a 1.5 : 1 AND WASTED UPPER LIMB male to female ratio (van den Berg-Vos et al. Clearly any patient with unexplained weak- 2003). Whatever the aetiological relationship ness and wasting of the upper limb merits MR of the conditions described in these different scanning of the cervical and upper thoracic series, this suggests that the clinical syndrome spinal cord to exclude a structural lesion, either of monomelic amyotrophy may be more com- intrinsic or extrinsic. The absence of sensory mon than previously appreciated in Europe and symptoms does not exclude a compressive my- have a much later onset, well into the age range eloradiculopathy. Some patients undergoing at which MND commonly presents. While it is surgery for apparent thoracic outlet syndrome usually stated that there are no upper motor continue to slowly progress, suggesting that neuron features and that the cranial nerves are focal motor neuron degeneration may have never involved, if case ascertainment is defi ned been responsible for their symptoms (Donaghy using these exclusion criteria, all such state- et al. 1999). © 2004 Blackwell Publishing Ltd 364 PRACTICAL NEUROLOGY Pract Neurol: first published as 10.1111/j.1474-7766.2004.00265.x on 1 December 2004. Downloaded from Somewhat confusingly, one of the most com- CAUSES OF UNILATERAL WASTING OF THE mon presentations of MND is with weakness and UPPER LIMB wasting of one limb, either foot drop or wasting of • Monomelic amyotrophy the small muscles of the hand. It will be apparent • Motor neuron disease/amyotrophic lateral sclerosis from the above clinical description that there are • Spinal muscular atrophy some features in the clinical pattern of Hirayama • Cervical cord structural lesion, intrinsic or extrinsic type monomelic amyotrophy that make the dis- • Brachial neuritis tinction from MND relatively straightforward • Multifocal motor neuropathy with conduction block after a period of time has elapsed. Most notably MND is by defi nition a more progressive disor- der. Fasciculations are common and proximal muscle wasting is often present within months of distal wasting appearing. However, there is no doubt that a monomelic onset of MND can remain confi ned to one limb for considerable periods of time, even years. This is further com- plicated by the fact that motor neuron disease restricted to the upper limb (so-called ‘brachial amyotrophic diplegia’) is characteristically of slower progression than typical MND, often run- ning a clinical course of 5–10 years. In most cases the latter disorder becomes bilateral soon after onset and involves more widespread proximal muscle groups than the more distal and restricted pattern outlined above for monomelic amyotro- phy. Most specialists in motor neuron disorders would probably agree that progression to MND can only conclusively be excluded if there is no progression beyond the upper limb within three years. However, at least the recognition that rela- tively non-progressive forms of weakness and wasting of one limb do exist should help avoid a premature diagnosis of MND. Clinical neuro- http://pn.bmj.com/ physiology may be helpful in demonstrating the more widespread involvement of limb or bul- bar muscles in MND, but minor EMG changes should never be used to secure the diagnosis if the clinical pattern is not consistent. on September 25, 2021 by guest. Protected copyright. The spinal muscular atrophies (SMA) are a heterogeneous group of diseases of genetic ori- gin and variable distribution characterized by slowly progressive pure lower motor neuron degeneration (Talbot & Davies 2003). Despite the presumed hereditary basis of most forms of lower motor neuron degeneration, appar- ently sporadic cases do occur, though autosom- The patient al recessive inheritance is diffi cult to exclude. A with particular form of dominantly inherited distal unilateral or SMA, which has recently been shown to be due asymmetrical to mutations in the glycyl tRNA synthase gene, upper limb shows predilection for the upper limbs. Anita wasting Harding coined the term ‘chronic asymmetrical presents a spinal muscular atrophy’ to describe a group of diagnostic patients with distal weakness and wasting, pre- challenge. dominantly of the upper limb (Harding et al. © 2004 Blackwell Publishing Ltd DECEMBER 2004 365Pract Neurol: first published as 10.1111/j.1474-7766.2004.00265.x on 1 December 2004. Downloaded from 1983). It is possible that some of these patients had a Hirayama-like amyotrophy.