Upper and Lower Motor Neuron Etiology

00:02 Now let's talk about some of the etiologies of motor neuron diseases.

00:05 What causes motor neuron disease? Well, we can divide this into things that affect the upper motor neurons, the lower motor neurons and both.

00:14 And certain conditions have a predilection for various types of motor nerves.

00:19 In terms of upper motor neuron pathology, here's a number of conditions that we consider and include on the differential diagnosis for those patients.

00:27 Hereditary spastic paraplegia is exactly what it says, it's a hereditary disorder, begins in often in middle age, it's inherited, and patients develop slowly and gradually progressive spasticity and paraplegia.

00:40 They're weak below the waist at a certain spinal level, it's motor predominant, there's not typically sensory findings which is unique.

00:48 In terms of its spinal cord presentation, patients become extremely spastic and acn have difficulty walking and ultimately often become wheelchair bound.

00:56 And unfortunately, there is no cure and supportive care is the optimal treatment for those patients.

01:02 Primary lateral sclerosis is a variant of ALS, it's a motor neuron variant that presents with primarily upper motor neuron symptoms.

01:10 Those patients don't have the lower motor neuron pathology.

01:13 The pathology is primarily in that first order motor nerve and so patients present with upper motor neuron findings.

01:20 Ischemic stroke is in the differential for an upper motor neuron lesion.

01:23 Strokes affect the brain, that's where the upper motor neurons are.

01:26 And so stroke patients can look in some respects like they present with an upper motor neuron pathology but the timeline of onset should really give away a stroke.

01:36 It's acute, it's a fixed deficit.

01:38 Whereas in typical motor neuron pathology, we see gradually progressive symptoms over time.

01:44 Spinal cord transection can present in this way and typically that would be due to trauma, which would be present on the history, and the Brown-Sequard syndrome is a spinal cord disorder that can present with prominent upper motor neuron pathology.

01:56 We also see lower motor neuron predominant conditions that look like the lower motor neuron variants of motor neuron disease.

02:03 Spinal muscle atrophy is an inherited disorder.

02:06 There are three types, one affecting very young children, infants and neonates.

02:10 Other affecting young children and then sometimes into adolescents or adults.

02:14 This is where there's degeneration of that second order motor neuron, the lower motor neuron and it degenerates over time.

02:20 Patients present with severe weakness, difficulty walking, fasciculations and atrophy - lower motor neuron pathology.

02:28 Historically there had not been a treatment for spinal muscle atrophy and in the last 5 to 10 years, there's been a new treatment.

02:34 Gene therapy that have revolutionized the treatment of this condition and really changed how we managed those patients.

02:40 In some states, testing for spinal muscle atrophy, a mutation in the SMN gene is now standard in terms of neonatal testing.

02:49 Distal hereditary motor neuropathies, the motor neuropathies can present like a lower motor neuron disorder.

02:56 Poliomyelitis is an infection that can affect all of the nerve roots in the spinal cord and cause a polyradiculoneuropathy so poly- meaning all of the nerves, -radiculo- meaning the nerve roots are affected not the nerves out in the hands, but the nerves in at the nerve root.

03:12 -neuropathy meaning many nerves are affected and so patients present with a diffuse lower motor neuron syndrome.

03:19 CSF testing would suggest a diagnosis of polio and those patients would be managed symptomatically.

03:25 We don't see a lot of poliomyelitis these days but in he era of he polio pandemic and epidemic, this was a common cause of a lower motor neuron syndrome.

03:34 Multifocal motor neuropathy is an inflammatory disorder of the motor nerves, Chronic inflammatory demyelinating polyneuropathy, is also an inflammatory disorder, and Guillain-Barre is an acute onset ascending rapid paralysis that can present with prominent motor symptoms and mimic a lower motor neuron disorder.

03:54 And then there's some combined conditions.

03:56 Lesions secondary to trauma can cause upper motor neuron findings below the level of the trauma.

04:01 Lower motor neuron findings at the level of the trauma and is a consideration.

04:05 Compression of the spinal cord from malignancy can again cause upper motor neuron findings below the level of the tumor.

04:11 Lower motor neuron findings at the level of the tumor and are important considerations.

04:16 And then we have the myeloneuropathies.

04:18 Vitamin B12 deficiency, copper deficiency and vitamin E deficiency can present with a myeloneuropathy or a combination of myelopathy, upper motor neuron symptoms and neuropathy, peripheral nerve nervous system symptoms, but often we see sensory changes in those patients which suggest alternative diagnoses other than motor neuron disease