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Hereditary Brachial Plexus Neuropathy

Hereditary Brachial Plexus Neuropathy
HBPN-presents with attacks of multifocal nerve injury affecting the upper limbs.
Attacks are acute or sub acute in onset, often associated with severe pain, significant morbidity and disability.
Pathophysiologic localization in unilateral or asymmetrical in the brachial plexus or nerves arising from the plexus or roots, without a more generalized peripheral neuropathy (distinguishing from HNPP-more generalized with focal changes).
Historical overview

1886 Dreschfeld described 43 year old female with 3 discrete episodes; termed “rheumatic peripheral neuritis” mentioned pt’s sister had similar attacks.
1961-Jacob et al. described in 7 pts in two unrelated families attacks.
Features of HBPN

Autosomal dominant with varied penetrance and expression.
Recurrent attacks.
Associated with stressors-pregnancy and parturition, mild trauma, infection, immunization.
Multifocal or patchy axonal degeneration of upper limb nerves, plexus, possibly roots, with inflammation in areas of degenerating fibers.
The most important feature between HBPN and sporadic form is family history.

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Hereditary Motor/Sensory Neuropathy Classification

Hereditary Motor and Sensory Neuropathy Classification
Based on clinical, electrophysiologic, and morphologic criteria·       HMSN I/CMT 1  “hypertrophic form”       demyelinating CMT;·       Usually autosomal dominant; recessive form more severe·       Pathology-nerve biopsy: segmental demyelination, onion-bulb formation, increase endoneural space, extensive loss of myelinated fibers.·       Slowly progressive distal weakness and wasting more prominent than sensory loss; areflexia distal or more generalized·       Foot deformity (pes cavus), gait disturbance, late childhood/early adulthood.  Scoliosis in more severe cases.·       Marked NCV reduction.

·       EMG:  positive sharp wave, fibrillation activity frequently; loss of motor unit recruitment pattern with sign of increased amplitude/duration MUPs with re-innervation.

·       HMSNII/CMT 2 “neuronal form”    neuroaxonal CMT;

·       Usually autosomal dominant, less severe than CMT1.

·       Pathology- biopsy: loss of larger axons, onion bulb formation absent. Demyelination rare, little loss of endoneural space.

·       NCV slowing not as marked.  May be in normal range.

·       EMG fasciculation, complex repetitive discharge activity more frequent.

·       EMG partial denervation

·       HMSN III          Dejerine-Sottas disease-early onset demyelinating;

·       Autosomal recessive

·       Motor/sensory peripheral neuropathy

·       Weakness, gait disturbance, sensory loss, decreased/absent DTR.

·       May be sensory ataxia.

·       NCV-marked slowing; sensory responses may be absent.

·       HMSN IV          Refsum Disease

·       HMSN V familial spastic paraplegia

·       HMSN VI          optic atrophy

·       HMSN VII        retinitus pigmentosa

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Herpes Virus Infection and Peripheral Neuropathy

  • All Herpes virus are DNA viruses
  • Eight human herpes viruses have been identified
    • Herpes Simplex Virus
      • HSV-1
      • HSV-2
    • Varicella Zoster Virus-VZV
    • Epstein-Barr Virus-EBV
    • Cytomegalovirus-CMV
    • Human herpesviruses
      • HHV-6
      • HHV-7
      • HHV-8


Herpes Simplex Virus

  • Primary HSV infection typically involves the oropharynx and genitals
  • Most infections are subclinical and followed by latency in ganglionic neurons
  • Periodic activation produces recurrent painful eruptions around the  mouth (HSV-1) and genitals (HSV-2)
  • Neurologic complications
    • Encephalitis – usually HSV-1
    • Aseptic meningitis and recurrent radiculopathy-usually HSV-2.
    • Myelitis-rare-HSV-2
    • HSV-1 associated with Bells Palsy
  • Latency
    • HSV-1 latency mostly restricted to cranial ganglia
    • Most humans have HSV-1 in their trigeminal ganglia
    • HSV-2 is latent primarily in the lumbosacral ganglia; reactivation produces genital herpes.
    • Extension of HSV-2 into the meninges may produce aseptic meningitis, often recurrent.
    • HSV-2 may manifest as sciatica or trigeminal distribution pain.
  • Diagnosis-amplification of viral DNA from CSF


Varicella Zoster Virus

HNPP-Hereditary neuropathy

Liability to Pressure Palsy
HNPP-Hereditary neuropathy with liability to pressure palsy·Autosomal dominant trait with total penetrance but variable expression.·       Deletion of the PMP-22 gene on chromosome 17.

·       Histopathology studies-tomaculous “sausage like” neuropathy.  Focal thickening of myelin sheaths, with apparent compression and flattening of axons at such sites.  May have extensive demyelination with re-myelination and onion bulb formation.

·       Clinical presentation-single or multiple nerve involvement.  May occur after mild compression or traction.  Symptoms may reduce, but neurologic abnormalities may persist.

·       Median, ulnar, radial, peroneal neuropathy common. NCV changes may occur in clinically unaffected nerves.

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Horner’s Syndrome

  • Caused by interruption of the ipsilateral sympathetic outflow to the head and neck.
    • Three neuron sympathetic outflow path must be intact to provide tonic output of norepinephrine at the effector cell.
      • Central cells origin in hypothalamus.
      • Axons traverse brainstem to spinal cord levels C7-T1.  Axons from intermediolateral  spinal column of the spinal cord provide 2nd step in the three-neuron arc.
      • From the spinal cord and beyond, the fibers form part of the peripheral nervous system.
        • Fibers proceed across the apex of the lung.
        • Fibers ascend to C3-C4 superior cervical ganglion, where they synapse and travel with the internal carotid artery into the cavernous sinus.
        • Sympathetic fibers join the abducens nerve, and then enter the orbit with the ophthalmic branch of the trigeminal nerve.




  • The combination of miosis and ptosis by itself is not particularly helpful in localizing the lesion.
    • It can result from lesions in the brainstem or spinal cord, damage at the lung and in the supraclavicular space, or damage to the carotid plexus along the internal carotid artery all the way to the cavernous sinus.
  • Clinical signs
    • Ptosis
      • Muller’s muscle-the sympathetically innervated retractor of the upper lid, is paralyzed in Horner’s syndrome, and this narrows the palpebral fissure.
      • The lower lid is has some sympathetically innervated fibers-causing some “upside down ptosis”
    • Miosis
      • Tiny pupil-is never intense
      • Paralysis of pupillodilator muscle causes only moderate decrease in the pupil size
    • Dilation lag
      • The slowness of the affected pupil to dilate is characteristic of Horner’s syndrome.
      • Can be of great clinical help in making the diagnosis.


Ischemic monomelic neuropathy

Ischemic monomelic neuropathy
·       Axonal loss neuropathy distal to occlusion of or shunt placement in a major artery in a limb.·       Ischemia related to decrease in arterial blood flow; ischemia insufficient to produce muscle necrosis.

·       NO clinical sign of vascular insufficiency, such as pallor or absent peripheral pulse.

·       EMG/NCS changes confined to affected limb.

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Late Responses

Late Responses

The H reflex
With recording electrodes over the soleus, and stimulation of the posterior tibial nerve at the popliteal fossa, a short latency CMAP is recorded as a direct response via orthodromic alpha motor axon stimulation.
In addition, an indirect, longer latency response may be recorded via Ia orthodromic stimulation through the reflex arc. This is referred to as the H-reflex.With a small intensity stimulus, the longer latency, indirect H reflex response may be evoked prior to the direct, shorter latency CMAP response, given the fact that the sensory axons are larger and more myelinated than the motor axons, and have a lower threshold of activation. In practice, it is difficult to evoke only an indirect H response, without the direct response, but the H reflex can usually be seen as a larger amplitude response than the direct response. After evoking the H reflex with a small intensity stimulus, increasing the stimulus intensity will inhibit the H reflex, but the CMAP direct response will continue to be seen. H reflex inhibition occurs through renshaw cell inhibition, collision between action potential mediated thru the Ia and antidromic alpha motor axons, or because the axon hillock may be in refractory period from the preceding antidromic alpha motor neuron mediated action potential.Clinically, the H reflex is readily obtained from the soleus, and serves as an evaluation of the S1 reflex arc. It is less reliably evoked from the flexor carpi radialis as a function of the C7 reflex arc.
In non-clinical setting, H reflex may be evoked from other muscles as well, with less reliability.

H-reflex (soleus recording) electrode set up

H reflex recording with small M wave

The F response
With recording from any muscles, and electrical stimulation of the nerve supplying that muscle, a direct CMAP response is evoked and recorded on the oscilloscope. This is the result of orthodromic activation of the alpha motor axons. Activation of the motor axons antidromically, with an action potential rebounding orthodromically from the motor cell body produces an indirect response, longer in latency than the direct response. This is known as the F response.The F response is mediated strictly up and down the alpha motor system. The fact that the F response continues to be seen in de-afferented limbs suggests that the response is not mediated through a reflex arc. Supramaximal stimulus facilitates the F response, whereas it will inhibit the H response.The F wave amplitude is much smaller than the direct CMAP amplitude, depending on which motor cell bodies fire back. The latency will also vary. Several F responses will be recorded, and the one with the shortest latency used for data.

The F wave latency allows for indirect evaluation of a proximal nerve segment. The proximal nerve segments can be technically difficult to assess nerve conduction velocity through standard techniques.

F response
F response with supramaximal evoked M wave

F response
 Antidromic stimulation of motor neurons (alpha motor neuron)
Conduction to and from spinal cord
No reflex involved; found in de-afferented limbs
Found in all skeletal muscles
Enhanced with supra-maximal stimulation
Low amplitude response ( less than 10% M response)
Variable latency, depending on which percent of motor neurons fire back
Indirect assessment of proximal conduction
H reflex
Electrical equivalent of the phasic muscle stretch reflex
Limited to ant-gravity muscles
Most commonly used to assess S1 nerve root integrity
H reflex amplitude, latency consistent with successive stimuli
Inhibited by supra-maximal stimulation
Collision from anti-dromic impulse of alpha motor neuron
Refractory period of axon hillock due to passage of preceding antidromic response
Renshaw inhibition

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McArdle Disease

McArdle Disease

McArdle disease (also known as glycogen storage disease type V) is a pure myopathy caused by an inherited deficit of myophosphorylase, the skeletal muscle isoform of the enzyme glycogen phosphorylase.

  • Glycogen storage disease V·
  • Autosomal recessive muscle disorder due to myophosphorylase deficiency·
  • Prototype of muscle glycogenosis manifested by exercise intolerance.·
  • In clinical setting, exercise related symptoms, including painful contractures, and, in about 50% of cases, rhabdomyolysis and myoglobinurea occur after brief strenuous isometric effort, or intense sustained dynamic exercise.·
  • Symptoms relieved by rest.·       Permanent weakness may occur.

Symptoms usually start later in life, affecting proximal greater than distal muscles

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Median Anastamosis

·     Martin Gruber-median to ulnar anastamosis

Median to ulnar nerve crossover in forearm.o      Motor fibers usually

o      Rare sensory cross over described.

·       1st described by Martin in 1763, and later by Gruber in 1870.

·       ? Autosomal dominant inheritance.

·       Reported incidence of 10-40% of median nerves.

·       Usually cross over fibers originate from the distal anterior interosseous nerve but other patterns described

o      Branch from proximal anterior interosseous nerve

o      Branch directly from median nv.

o      Branch from AIN to ulnar FDP.

o      Branch from AIN to join ulnar nerve at more than one site.

·       Type I-crossover fibers terminate in hypothenar muscles.

o      Ulnar NCS- may observe ulnar pseudo-conduction block in the forearm-more fibers stimulated at wrist with higher CMAP than proximal forearm or above elbow stim.

·       Type II-crossover fibers terminate in first dorsal interossei innervation.

o      Most common.

o      Again-ulnar NCS result in higher CMAP with wrist stim than proximal to crossover.

·       Type III-crossover fibers terminate in thenar muscles.

o      Least common.

o      Median NCS-larger CMAP with elbow stim than wrist stim.

·       Martin-gruber anastamosis with carpal tunnel syndrome

o      Initial positive deflection CMAP with elbow stim-always indicative of carpal tunnel syndrome (Guttman)

o      May have erroneous high NCV-very short latency with elbow stim-these fibers not impeded at carpal tunnel.

Marinacci Anastamosis

·       Ulnar to median motor cross over in forearm or wrist.

Riche Cannieu anastamosis

·       Ulnar deep motor crossover to median nerve in palm.

·       Incidence

o      6/16 hands in one dissection

o      27/35 hands in another.

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Monoclonal Gammopathy

Neuropathy Associated with Monoclonal Gammopathy
·       A small number of healthy people have an abnormal protein (monoclonal protein or M protein) in their blood. Monoclonal gammopathy of undetermined significance (MGUS), is benign and usually causes no problems. On occasion, monoclonal gammopathy of undetermined significance progresses over decades to other disorders, including some forms of cancer.·       Each monoclonal protein produced by a clone of plasma cells in the blood. Important to differentiate mono from polyclonal.  Monoclonal protein has possible malignant origin; polyclonal increase has inflammatory or reactive process.·       Presence of monoclonal protein (immunoglobulin G, A, or M), in the serum of pt with peripheral neuropathy raises suspicion of POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes), as well as multiple myeloma, macroglubulinemia, or lymphoma.

·       Presence of M protein may also be benign-“monoclonal gammopathy of undetermined significance” or MGUS.

·       Cause of peripheral neuropathy with monoclonal gammopathy is unknown.  Genetics may play a role.

·       Pathology:  The IgM monoclonal protein with anti-MAG activity associated with peripheral neuropathy reacts or binds to the myelin sheaths.  Loss of fibers, wallerian like degeneration, and segmental demyelination were found in the peroneal superficial nerve of a pt with an IgM monoclonal gammopathy and peripheral neuropathy.

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Ray Jurewicz
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