The neurologic approach
Stanley Berent, James W. Albers in Neurobehavioral Toxicology, 2012
Nerve conduction studies are non-invasive means of evaluating electrochemical signals generated by peripheral nerve or muscle in response to percutaneous electrical stimuli. The sensation produced by the stimulating electrode resembles a static electricity ‘carpet shock’. Supramaximal stimuli, sufficient to depolarize all the fibers in a given nerve, generate signals in the form of sensory and motor responses that can be recorded from the surface of the extremities and head using surface electrodes. Important characteristics of these signals include amplitude and conduction velocity of the largest myelinated nerve fibers. Distal latencies are measured in the nerve terminal, where conduction is slower than along the more proximal portions of nerve. Conduction times over the entire length of a motor nerve are evaluated by F-wave latency. F-waves represent an antidromic motor nerve stimulation that travels from the periphery to the spinal cord, where a portion of the motor neuron pool is activated, sending an orthodromic motor response back along the same motor fibres initially activated. The F-wave latency represents a summation of the time necessary for the action potential to travel along the entire length of the motor nerve twice, to and from the spinal cord along a motor fiber. The long distance over which the measurement is made accentuates mild generalized slowing (Daube, 1987).
Accident and Emergency
Nagi Giumma Barakat in Get Through, 2006
This is a group of genetic neuropathies with an incidence of 10 per 100 000 of the population. The commonest is HMSN type 1: Charcot-Marie-Tooth disease. It is autosomal dominant, with peroneal atrophy. In many cases, the abnormal gene is on chromosome 17. The initial symptoms are either foot deformities or gait disturbances beginning in the 2nd decade and sometimes in early infancy. Pes cavus is typical, and hammertoes may be present. All of these weaknesses are caused by weakness of the intrinsic foot muscles. Gait is described as a neuropathic gait, with the feet being lifted up and dropped on the floor, and the child is described as clumsy. Initially, examination will show atrophy of the peroneal muscles, pes cavus and reduced reflexes of the Achilles tendon. The disease is progressive and leads to more muscle weakness that may affect the proximal and distal muscles, foot drop and cramps with normal sensation. In adults, peripheral nerves are enlarged, which is caused by repeated episodes of demyelination and remyelination. Nerve conduction studies are diagnostic, along with a muscle biopsy in cases with a normal nerve conduction study. There is no specific treatment, but supportive care with proper foot care should be given.
The Problems
John Greene, Ian Bone in Understanding Neurology a problem-orientated approach, 2007
These neurophysiological studies address different questions. Electromyography (EMG) detects the electrical activity of muscle fibres using a needle inserted into resting and active muscle. The pattern of activity changes if there is ongoing denervation, damage to muscle membranes, or abnormally small muscle fibres. It also allows the detection of the large motor units seen in disorders where denervation is followed by reinnervation by surviving motor axons (124). Nerve conduction studies (NCS) use electrodes to record from both motor and sensory nerves. In usual practice, only myelinated axons are studied. Information is gathered on conduction velocity and the amplitude of the nerve impulse under study. The findings often allow a distinction to be made between disorders affecting the axon and those affecting the myelin sheath. They also allow motor and sensory fibre populations to be studied independently.
The role of dietary non-heme iron load and peripheral nerve inflammation in the development of peripheral neuropathy (PN) in obese non-diabetic leptin-deficient ob/ob mice
Published in Neurological Research, 2019
Joanna Kosacka, Katrin Woidt, Klaus V. Toyka, Sabine Paeschke, Nora Klöting, Ingo Bechmann, Matthias Blüher, Joachim Thiery, Susann Ossmann, Petra Baum, Marcin Nowicki
We performed nerve conduction studies at the beginning and at the end of the experimental period. Sciatic nerve MNCVs of all ob/+ groups increased mildly throughout the experiment as expected with further maturation in control mice. Motor NCVs (MNCVs) of ob/ob mice significantly declined with all iron diets (Figure 1(a and b)). When compared to the ob/+ control animals, sciatic MNCVs were reduced in ob/ob mice with different iron diets by up to 24% (Figure 1(e)). This indicates that conduction was abnormally slowed rather than halted by a lack of further nerve maturation. The sciatic compound sensory NCVs (cSNCVs) were already by about 30% lower in all ob/ob mice at age 3 months before any dietary treatment started as compared to the ob/+ controls (Figure 1(c and d)). At the end of the study, the sciatic cSNCVs had significantly decreased in all ob/ob mice as compared to the respective control animals (Figure 1(f)). In contrast to MNCV, the cSNCVs did not increase over the experimental period in the control mice. The highest cSNCV decrease (by up to 45%) was observed in ob/ob animals on a low iron diet (Figure 1(f)).
Chameleons, red herrings, and false localizing signs in neurocritical care
Published in British Journal of Neurosurgery, 2022
Boyi Li, Tolga Sursal, Christian Bowers, Chad Cole, Chirag Gandhi, Meic Schmidt, Stephan Mayer, Fawaz Al-Mufti
Radiculopathy is a nerve root dysfunction that causes sensory or motor symptoms. Common etiologies include mechanical compression, neuropraxia or chemical irritation of nerve roots.71 Though rare, radiculopathy has been reported as a FLS in intracranial hypertension, particularly in IIH, central venous sinus thrombosis (CVT), and intracranial sinus venous thrombosis (ISVT).8,72 One pathophysiology of this type of radiculopathy is similar to that of cranial nerve neuropathies in intracranial hypertension: elevated ICP in the subarachnoid space causing compression of nerve roots.7,72 Motor roots may be more susceptible to damage as patients tend to have normal sensorium.8,72 Patients can present with headache, papilledema, progressive visual loss, complete ophthalmoplegia, flaccid areflexic quadriparesis, as well as motor weakness and leg pain presenting primarily in herniated lumbar disc patients.8,72 Radiculopathy can be confirmed by electrophysical findings and normal MRI of brain and spinal cord, as well as normal angiography, can exclude other possibilities such as midbrain infarction secondary to deep cerebral venous thrombosis and cavernous sinus thrombosis.8 To avoid misdiagnosis, nerve conduction studies should be viewed carefully, in context with imaging and other ancillary testing.
Early diagnosis of ATTR amyloidosis through targeted follow-up of identified carriers of TTR gene mutations*
Published in Amyloid, 2019
Isabel Conceição, Thibaud Damy, Manuel Romero, Lucía Galán, Shahram Attarian, Marco Luigetti, Menachem Sadeh, Stayko Sarafov, Ivailo Tournev, Mitsuharu Ueda
A clinical questionnaire for ATTR amyloidosis will incorporate sensorimotor symptoms such as paraesthesia and loss of temperature sensation, as well as autonomic symptoms such as gastrointestinal problems and sexual dysfunction. Clinical examination should include neurological examination using the Neuropathy Impairment Score (NIS, a composite score of specific items of the neurological examination that assess muscle weakness and loss of reflex and sensation), small-fibre neuropathy and symptom inventory questionnaire (SFN-SIQ). Neurophysiological assessments that may be used include electromyography with nerve conduction studies, sympathetic skin response and quantitative sensory testing [15]. Tests of autonomic function include postural blood pressure monitoring, sudomotor testing and heart rate (R-R) variability [10].
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