Discussion
The patient’s initial neurological syndrome was atrophy of the right
leg. The first diagnosis was made between monomelic amyotrophy, spinal
muscular atrophy, progressive muscular atrophy, and multifocal motor
neuropathy. MMA is characterized by signs of spinal cord atrophy and
vertebral canal stenosis, which was not detected on MRI, as well as the
absence of sensitive disturbances [3]. SMA is characterized by
symmetrical atrophy, when patient suffered amyotrophy and muscle
weakness only in right leg for long time. EMG revealed no conduction
blocks, and there was low titer for GM-1 and GM-2 antibodies, which made
it possible to exclude MMN [4]. As the disease progressed, symptoms
of upper motor neuron damage developed, such as brisk reflexes and
pathological signs. EMG showed signs of damage to the motor neurons of
the anterior horns of the spinal cord in the segments outside the
affected right leg. Finally, in 2015 the combination of LMN and UMN
clinical signs of one lumbar region, EMG LMN signs in lumbar and cervic
regions, made it possible to diagnose clinically probable laboratory
supported ALS according to the revised El-Escorial criteria concurrent
with hydromyelia [2]. In 2019 the diagnosis was changed to possible
ALS.
We have wondered whether the revealed central canal dilation has a
clinical manifestation in this patient. Our clinical experience allows
us to state that the dilation of the central canal with such small
diameter without increasing over time cannot cause progressive severe
paresis and atrophy of the lower limb [5].
The origin of the central canal dilation is unclear. The MRI showed no
Chiari malformation or other extramedullary factors predisposing to
syringomyelia. In addition, there was no history of spinal cord trauma,
inflammatory processes, infarction or hemorrhage. We suppose that the
presence of hydromyelia is a casual association. For example, Holly and
Betzdorf (2002) argued, that slit-like syrinx cavities are remnants of
the central canal and can be found in a small percentage of adults
[6]. Patients with slit-like syrinx could be neurologically intact
or just report the pain in different distributions. Petit-Lacour et al.
(2000) demonstrated the incidence of asymptomatic slit-like syrinx could
reach approximately 1.5% [7]. Follow-up imaging reveals no changes
in cavity size.
However, we have found some case reports of neurodegenerative diseases
concurrent with hydromyelia. In one case, Masciullo et al. (2016)
described a patient with SPG56 – rare form of hereditary spastic
paraplegia, caused by mutations in CYP2U1 and concurrent with
hydromyelia [8]. The authors proposed that the presence of
hydromyelia is not a casual association, but it may be part of the
phenotype of SPG56. The authors supposed the hydromyelia in these cases
is linked to mitochondrial dysfunction. It supported by the cases of
hydromyelia described in patients with CMT2A and harboring mutations in
MFN2 [9]. In the study Bombelli F. et al. have found an involvement
of the CNS in the pathological process in these patients with CMT2A:
26% of patients develop CM abnormalities, 9% of patients develop
hydromyelia. The authors also believe that the spinal cord cavity in
these patients is not a coincidence, but is part of the phenotype. Both
CYP2U1 and MFN2 encode enzymes regulating energy metabolism and
mitochondrial dynamics. In recent ALS reviews mitochondrial dysfunction
is indicated as one of the pathogenic links [10].