ALS Median neuropathy
Amyotrophic Lateral Sclerosis MGUS polyneuropathy
Anterior Interosseous Syndrome MMN
Arthrogryposis Multiplex Mononeuropathy
Axillary neuropathy Multifocal Motor Neuropathy with Conduction Blocks
Botulism Muscular Dystrophy
Brachial plexopathy Musculocutaneous neuropathy
Carpal Tunnel Syndrome Myasthenia Gravis
Cervical radiculopathy Myopathy
Chronic Immune Demyelinating Polyneuropathy Neuropathy
CIDP Obturator neuropathy
Cubital Tunnel Syndrome Pelvic girdle neuropathy
Dermatomyosits Peroneal neuropathy
Dorsal Scapular neuropathy Plantar neuropathy
Entrapment syndromes Plexopathy
Facio-scapulo-peroneal SMA Polymyositis
Fazio-Lande SMA Polyneuropathy
Femoral neuropathy Posterior Interosseous Syndrome
GBS Pronator Teres Syndrome
Gluteal neuropathy Radial neuropathy
Guillain-Barre Syndrome Radiculopathy
Guyon’s canal entrapment Scapulo-peroneal SMA
Handcuff neuropathy Sciatic neuropathy
Inclusion Body Myositis Shoulder girdle mononeuropathy
Infantile SMA SMA
Juvenile bulbar SMA Spinal Muscular Atrophy
Juvenile SMA Stiff Person Syndrome
Kugelberg-Wellander SMA Suprascapular neuropathy
Lambert-Eaton Syndrome Tarsal Tunnel Syndrome
Lateral Femoral Cutaneous neuropathy Tibial neuropathy
Long Thoracic neuropathy Ulnar neuropathy
Lumbar plexopathy Ulnar palmar branch neuropathy
Lumbar radiculopathy Werding- Hoffman SMA
 

Amyotrophic Lateral Sclerosis
 
Muscle wasting in ALS is a result of anterior horn cell degeneration, thus the essential electrophysiologic features include sparing of the sensory fibers with a widespread affliction of motor neurons. EMG showed active denervation (axonal loss) with evidence of chronic reinnervation crossing the individual myotomes.
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Lateral Femoral Cutaneous neuropathy
   


Lateral Femoral Cutaneous (LFC) mononeuropathy (Meralgia Paresthetica) causes sensory symptoms in the lateral portion of the thigh. Differential diagnosis includes lumbar radiculopathy. Sensory nerve conduction of the LFC nerve is somewhat difficult to obtain, especially in obese patients.
   
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Lambert – Eaton Syndrome
   
Lambert – Eaton Myasthenic Syndrome (LEMS), in which a pre-synaptic release of acetyl-choline is blocked, a marked increment is seen on the repetitive stimulation test (RST). This feature can differentiate this condition from Myasthenia Gravis in which a decrement is seen on the RST. Botulism cam also cause an incremental response on RST, but the increment is usually lesser then in LEMS.
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Median neuropathy
   
Median mononeuropathy at the wrist (CTS) is the most common mononeuropathy in clinical practice. In addition to evaluating for presence and severity of CTS, the role o the EMG is to exclude a neurogenic co-morbidity. Furthermore, as a pre-operative workup it establishes a very useful electrophysiologic baseline. In a situation where an unwanted post-operative outcome is seen, the absence of preoperative values precludes an assessment of the interval change. When available, a meaningful comparison can be made (electrophysiologic worsening, improvement or no change) which in turn can assist in a decision making process about a possible re-exploration of the carpal tunnel.

Possible sites of lesion for the median nerve include:


 

• Pronator Teres Syndrome (pain over the PT muscle; mimics CTS, weakness of APB and Flexor Pollicis; Normal distal NCS; EMG of PT normal while distal muscles abnormal)

• Anterior Interosseous Syndrome (pain in the forearm; no sensory deficits; inability to make OK sign; Normal NCS and EMG of FPL, FDP I and Pronator Quadratus)

• CTS (10% of population affected; frequently neglected in clinical practice; distal NCS abnormal; EMG of APB abnormal)

• Digital nerve lesion

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Mononeuropathies
   
NCS/EMG is very helpful to pinpoint the exact location of the lesion and to exclude a polyneuropathy, radiculopathy or plexopathy. Varieties of techniques are available for evaluation of individual nerves.

The mononeuropathies which could be seen in the upper extremities and shoulder girdle are:

In the lower extremities common neuropathies include:

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Myasthenia Gravis
   

Myasthenia Gravis is the most common disorder of the neuromuscular junction. It is characterized by muscular fatigability after exercise. Repetitive stimulation test is an electrodiagnostic technique used to evaluate for this condition. Furthermore, single fiber EMG can be performed in a situation where repetitive stimulation test is inconclusive.
   
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Myopathy
   
Myopathic conditions can be acquired or genetic. Most frequent clinical presentation includes proximal weakness. EMG shows small, polyphasic motor units with an “early” recruitment pattern. EMG diagnosis is anatomic, thus specific etiology must be determined:
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Pelvic girdle mononeuropathies
   
Lesions of the individual branches of the lumbar plexus are most frequently due to trauma. Differential diagnosis with lumbo-sacral radiculopathy is the most frequent question for the electromyographer.

Pelvic girdle mononeuropathies include:

  • Superior and Inferior Gluteal (Gluteus Medius and Gluteus Maximus; EMG abnormal)

  • Obturator (rare syndrome; Adductors and Gracilis; EMG abnormal)

  • Femoral (Quadriceps and possibly Iliopsoas depending on the site of lesion; NCS and EMG abnormal)

  • Lateral femoral cutaneous (pure sensory; abnormal sensory NCS; technically difficult NCS)

  • Sciatic (Hamstrings with sparing of Gluteus Maximus and paraspinals thus excluding S1 lesion; NCS and EMG abnormal)

 
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Peroneal neuropathy
   
Peroneal mononeuropathy is the most commonly seen with compression at the fibular head. The most common differential diagnosis includes L5 radiculopathy. EMG can show the exact localization of the lesion and evaluate for an axonal vs. demyelinating type of injury.
  • Abnormal NCS with slowing across the fibular head
  • Abnormal EMG (TA and EDB with sparing SHBF, TP, TFL and paraspinals thus excluding L5 lesion)

Another site of a possible lesion is distal to the Tibialis Anterior branch, which is a common issue in elderly secondary to a chronic trauma to the Extensor Digitorum Brevis.

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Plexopathies
   
Brachial and Lumbar plexopathies represent a complex anatomical diagnostic challenge. Differential diagnosis most frequently includes: Root lesion vs. Plexus lesion vs. “Double Crush Syndrome”. The EMG abnormalities in motor AND sensory NCS are seen, as the lesion is distal to the Dorsal Root Ganglion. EMG changes on needle examination are seen in the appropriate brachial truck or cord distribution without paraspinal muscle involvement.
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Polyneuropathies
   
The role of the NCS/EMG is to establish the presence of a polyneuropathy, define the fiber type affliction (i.e. pure sensory, pure motor, sensory-motor), determine the possible pathological process (axonal vs. demyelinating), and to exclude other conditions which could clinically present in a similar fashion. The ultimate goal of a polyneuropathy workup is to establish the etiology, and potentially offer treatment. NCS/EMG testing is a very powerful tool in reaching such goal. Relatively recent scientific advances in the field of immune mediated neuromuscular disease have established a very important role of NCS/EMG in diagnosing conditions such as Chronic Immune Demyelinating Polyneuropathy, Multifocal Motor Neuropathy with Conduction Blocks, Guillain-Barre Syndrome and MGUS associated polyneuropathy.
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Radial neuropathy
   
The most common lesion of the radial nerve is at the spiral groove of the humerus due to external pressure of a fracture. Another radial neuropathy of frequent medico-legal interest is a pure sensory neuropathy at the wrist caused by pressure form handcuffs. This can be easily documented by performing nerve conduction studies.

Possible sites of lesion for the radial nerve include:

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Radiculopathies
   
Radiculopathies are very frequently encountered in clinical practice. The most common deferential diagnosis includes:

Non-Neuromuscular (orthopedic) Lesions:

  • Muscle strain/sprain
  • Rotator cuff tendonitis/tear
  • Subacromial/trochanteric bursitis
  • Epicondylitis
  • Degenerative joint disease

Neuromuscular Lesions:

  • Motor neuron disease
  • Brachial and Lumbosacral Plexopathy
  • Mononeuropathy
  • Polyneuropathy

Cervical Radiculopathies:

  • C5: 2 - 14%

  • C6: 19 - 25%

  • C7: 56 - 70%

  • C8: 4 - 12%

Lumbar Radiculopathies:

  • L2/3

  • L4

  • L5 : most common

  • S1: second to L5

 
The goal of the EMG is to localize the compressed, and to establish the presence or absence of active axonal loss and/or chronic reinnervation changes. A very important role of the NCS/EMG is to evaluate for presence of a “Double Crush Syndrome”, in which a distal mononeuropathy is superimposed. The electrophysiologic abnormalities in radiculopathies include:

Possible abnormalities in motor NCS

  • Normal sensory NCS (lesion is proximal to DRG)
  • Possible active denervation in appropriate myotome and paraspinals
  • Very important limitations of EMG in radiculopathies are:
  • Absence of abnormalities in acute lesions (< 2 weeks)
  • “Normal” EMG in purely demyelinating lesions (no denervation)
  • “Normal” EMG in lesions limited to the sensory nerve root
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Shoulder girdle mononeuropathies
   
Isolated lesion of the individual nerves of the brachial plexus can occur due to fractures, intramuscular injections, shoulder dislocation or an infectious process. Supraspinatus nerve entrapment can be related to a ganglion or rheumatoid disease. EMG can differentiate if an entrapment is present at the spinoglenoid notch, affecting only the Infraspinatus muscle. These mononeuropathies clinically present as pain and weakness of the individual muscles thus the electrophysiology relies and the needle EMG examination

Shoulder girdle mononeuropathies include:

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Spinal Muscular Atrophy
   
Various types of Spinal Muscular Atrophy show the same or similar electrophysiologic findings consisting of fibrillations, positive sharp waves, large motor units and a reduced recruitment pattern.

 
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Stiff Person Syndrome
   
Stiff Person Syndrome is an acquired condition with fluctuating muscle stiffness and spasms. It begins in the axial muscles and progresses to involve proximal leg muscles. EMG shows that the stiffness is caused by motor unit activity at rest. Two thirds of patients have antibodies to glutamic-acid-decarboxylase (GAD).
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Tarsal Tunnel Syndrome
   

Tarsal Tunnel Syndrome (TTS) is an entrapment of the tibial nerve at the ankle which clinically presents as pain and sensory disturbance in the plantar aspect of the foot and big toe.

 

Plantar nerve neuropathies are seen with entrapment at the ankle or more distally in the foot. Standard nerve conduction techniques are available for testing of the medial and lateral plantar nerves.
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Ulnar neuropathy
   
The EMG in ulnar nerve lesions can establish the location of the pathological process, document the severity and evaluate for common differential diagnosis which includes lower trunk brachial plexopathy and C8 radiculopathy.

Possible sites of lesion for the ulnar nerve include:

  • Cubital tunnel syndrome (sensory symptoms in the 4th and 5th digit; weakness of FDI and ADM; abnormal NCS and EMG of FDI and ADM with sparing of FCU)
  • At Guyon’s canal (sensory deficit spares dorsum of the hand; weakness of the FDI and ADM; abnormal ulnar sensory NCS with normal dorsal ulnar cutaneous NCS)
  • Palmar branch (pure motor affliction of the FDI; NCS to the FDI abnormal and normal to the ADM; EMG of the FDI abnormal)
  • Digital nerve lesion
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