Discussion
This case complements our first clinical case of a 36-years male patient suffering from ALS with a dilated central canal of the thoracic spinal cord. Both clinical cases share such features as the slow progression of the disease, with manifestation in the lower limbs, and the presence of a cavity in the spinal cord. At the same time, these cases differ from each other in their initial main leading syndrome. When in the first case the initial syndrome is lower monoparesis with the atrophy, in the second — spastic lower paraparesis. Spastic paraparesis is a condition requiring differentiation with a wide range of pathologies, including spondylogenic myelopathy, demyelinating disorders (multiple sclerosis, neuromyelitis optica), vascular diseases (spinal cord infarction, arteriovenous shunts) and neurodegenerative diseases (hereditary spastic paraplegia, primary lateral sclerosis), etc. [11].Spondylogenic myelopathy, demyelinating and vascular disorders were excluded by the brain and the spinal cord MRI that did not show any typical sign. Our patient developed symptoms (spastic paraparesis and urinary urgency) matching uncomplicated HSP except for sensory signs. PLS is the diagnosis of exclusion and general features include the clinical presence of upper motor dysfunction most commonly in the legs, and the absence of sensory signs, marked fasciculation and muscle atrophy. EMG is usually normal, but can reveal minimal denervation that does not fulfill El Escorial criteria [12].
Our patient developed notable limbs amyotrophy, marked tongue fasciculation, and EMG data met El Escorial criteria, therefore HSP and PLS were excluded. Given all the data in 2015 clinically probable laboratory supported ALS was diagnosed according to revised El Escorial criteria [2]. It was changed to possible ALS in 2017 and definite ALS in 2019.
In this case, the question of the cause of the cavity also arises. In the first case, we decided that the most likely one is just a coincidence. This patient has signs of narrowing of the spinal canal on MRI (vertebrae’s front-rear size is less than size of vertebral canal). There is no history of the spinal cord damage. So we suppose the origin of central canal dilation is slightly narrow of vertebral canal, and this cavity can be classified as noncommunicating central canal dilation [13]. Also we suppose that such small cavity does not have a contribution in clinical manifestation. During 2014-2019, the cavity remained at the same size, despite a dramatic clinical deterioration in the last 2 years.
In the literature we have not met reports of cases of the ALS with hydromyelia, it has to be a very rare combination. But taking into account the fact that hydromyelia is a phenotypic feature of some neurodegenerative diseases [8, 9], there is the possibility that hydromyelia may be a part of the phenotype in the rare cases of ALS. Further observations are required.