ROUTINE NERVE CONDUCTION STUDY

Routine nerve conduction studies are performed to screen major nerves in both upper and lower limbs to get an idea about their normal function. The study is modified depending upon the clinical diagnosis or as requested by referring doctors (which are usually physicians, orthopedic surgeons, neurosurgeons or neurologists).

A routine test includes motor conduction studies performed on median and ulnar nerves in upper limb and posterior tibial and peroneal nerves in lower limbs. Sensory conduction studies are performed on median and ulnar nerves in upper limbs and sural nerves in lower limbs.

Therefore, if patient presents with wrist drop, then radial motor and sensory conduction study may be needed in addition to the above mentioned studies. Similarly, if patient presents with foot drop, superficial sensory studies may be required.

ELEMENTS OF NORMAL SLEEP ACTIVITY - POSTERIOR OCCIPITAL SHARP TRANSIENTS (POSTs)

Shape
Mono- or biphasic triangular waves.

Amplitude
30-50 µv

Frequency / duration
Variable, from 1 Hz to 4-6 Hz

Distribution
Occipital

Persistence
They may last up to few seconds, and are seen mainly in stages 1, 2 & 3 of NREM sleep

Synchrony
After 2 years of age, they are bisynchronous and symmetrical


Reference:

1. Erwin, CW, Somerville, ER and Radtke, RA. A review of electroencephalographic features of normal sleep. J. Clin. Neurophysiol. 1:253-274
2. Fisch BJ. Spehlmann’s EEG primer, Amsterdam: Elsevier, 3rd edition
3. Niedermeyer E, Lopes da Silva F. Electroencephalography: basic principles, clinical applications and related fields, Baltimore, Maryland: Williams and Wilkins, 4th edition

ELEMENTS OF NORMAL SLEEP ACTIVITY - SLEEP SPINDLES

Shape
Group of rhythmic waves characterized by gradually increasing and decreasing amplitude.

Amplitude
Usually less than 50 µv, may decrease with age



Frequency / Duration
12-14 Hz / Duration more than 0.5 seconds

Distribution
They are characteristically frontocentral in location

Persistence
They may last up to few seconds, and are seen in mainly stages 2 and 3 of NREM sleep

Synchrony
After 2 years of age, they are bisynchronous and symmetrical

Miscellaneous

1. Sleep spindles are usually well developed by 3-6 months of age, appearing in prolonged runs lasting 8s or longer separated by interval of less than 10 s. After that time, the duration of spindle bursts decreases.
2. Spindles are commonly asynchronous over the two hemispheres until the age of 8 months in normal infants; continuously asynchronous spindles after 2 years of age are abnormal.
3. Spindle bursts are fairly asymmetrical in normal infants, but a marked and persistent reduction on one side may suggest ipsilateral cerebral dysfunction.
   

Reference:

1. Hughes JR. Sleep spindles revisited. J. Clin. Neurophysiol. 2: 37-44.


2. Jankel, WR and Niedermeyer, E. Sleep spindles. J. Clin. Neurophysiol. 2: 1-36.


3. Fisch BJ. Spehlmann’s EEG primer, Amsterdam: Elsevier, 3rd edition


4. Niedermeyer E, Lopes da Silva F. Electroencephalography: basic principles, clinical applications and related fields, Baltimore, Maryland: Williams and Wilkins, 4th edition

COMMON PERONEAL NERVE ANATOMY

Sciatic nerve originates form the L4 thru’ S2 roots. It leaves pelvis by passing thru’ the greater sciatic foramen and enters thigh. In the upper popliteal fossa, it divides into common peroneal and tibial nerves. Within the sciatic nerve, the fibers that eventually form the common peroneal and tibial division run separately from each other.

In the upper thigh, tibial division provides innervation to all hamstring muscles except short head of biceps femoris which is supplied by the peroneal division. Thus, short head of biceps femoris is the only peroneal innervated muscle above knee joint.

Soon after separating from tibial division, the common peroneal gives off the lateral cutaneous nerve of the calf, which innervates the skin over the upper third of the lateral aspect of the leg (not highlighted in figure). Then the peroneal nerve winds around the fibular neck and divides into its terminal braches, the superficial and deep peroneal nerves.







Superficial peroneal nerve
The superficial peroneal nerve is predominantly sensory; it innervates the skin of the lower two thirds of the lateral aspect of the leg and the dorsum of the foot and sends motor branches to the peroneus longus and brevis.














Deep peroneal nerve
The deep peroneal nerve is predominantly motor; it innervates tibialis anterior, extensor hallucis, extensor digitorum longus & brevis (all ankle and toe extensors) and peroneus tertius. It sensory branches supply the skin of the web space b/w the first and second toe.


Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition
   
2. Preston DC. Distal Median Neuropathies. In: Entrapment and other focal neuropathies; Neurologic Clinics: WB Saunders company, August 1999
   
3. Katriji MB, Wilbourn AJ. Common peroneal neuropathy: a clinical and electrophysiologic study of 116 lesions. Neurology 1988;38:1723.

ELEMENTS OF NORMAL SLEEP ACTIVITY - K COMPLEXES

SYNONYM = K WAVE
Shape
Consist of an initial sharp component, followed by a slow component that fuses with a superimposed fast component. It may or may not be followed by sleep spindles. It is easily differentiated from vertex waves by longer duration and greater complexity and variation.

Amplitude
More than 200 µv in monopolar

Duration
More than 500 ms

Distribution
Frontal and vertex region

Persistence
They are seen at irregular intervals in stages 2, 3 and 4 of NREM sleep.

Synchrony
Bisynchronous

Miscellaneous

1. V waves and K complexes appear in well developed from for the first time at the age of 5-6 months.


2. They can be elicited during sleep by sensory stimulation (particularly auditory). The positive component usually occurs 0.75 seconds after the stimulus.

Reference:

1. Fisch BJ. Spehlmann’s EEG primer, Amsterdam: Elsevier, 3rd edition


2. Niedermeyer E, Lopes da Silva F. Electroencephalography: basic principles, clinical applications and related fields, Baltimore, Maryland: Williams and Wilkins, 4th edition


3. Stern JM, Engel J. Atlas of EEG patterns, Philadelphia: Lippicott Willams & Wilkins
   
   

ELEMENTS OF NORMAL SLEEP ACTIVITY – VERTEX WAVES

SYNONYMS = V WAVES, VERTEX SHARP TRANSIENTS
Shape
Sharp contoured compounded potentials

Amplitude
Up to 250 µv

Frequency / duration
Less than 2 Hz / Duration less than 200 ms

Distribution
Maximum at vertex (C3, C4) but may have wider distribution

Persistence
They are seen at irregular intervals in stages 1 and 2 of NREM sleep

Synchrony
Bisynchronous, may be unilateral

Miscellaneous

• V waves and K complexes appear in well developed from for the first time at the age of 5-6 months.
• They are most likely secondarily to auditory evoked potentials that converge from their cortical projection areas to a region underlying the vertex electrodes.

Reference:
1. Fisch BJ. Spehlmann’s EEG primer, Amsterdam: Elsevier, 3rd edition
2. Niedermeyer E, Lopes da Silva F. Electroencephalography: basic principles, clinical applications and related fields, Baltimore, Maryland: Williams and Wilkins, 4th edition
3. Jasper R. Daube. Clinical Neurophysiology, Philadelphia: F. A. Davis Company
4. Kooi, K. A. et al. Polarity and field configuration of the vertex components of the human auditory evoked response: a reinterpretation. Electroencephalogr. Clin. Neurophysiol. 31:166-169

RADIAL NERVE ANATOMY

The radial nerve is the largest branch of the brachial plexus. The radial nerve is derived primarily from the C5, C6, C7, C8 and T1.
The radial nerve enters the arm from axilla along the medial side of the humerus to reach the spiral groove. From the axilla to the spiral groove, the radial nerve gives off motor branches to triceps and anconeus. It also receives the posterior cutaneous nerve of the arm, the posterior cutaneous nerve of the forearm and the lower lateral cutaneous nerve of the arm in this region.
At the spiral groove, the radial nerve is in contact with the humerus as the nerve travels laterally, and then it pierces the lateral intermuscular septum. Here, it is bordered medially by the brachialis (Br) muscle, and laterally (from proximal to distal) by the brachioradialis (BR), the extensor carpi radialis longus (ECRL), and the extensor carpi radialis brevis (ECRB). All these muscles receive motor supply from radial nerve. The radial nerve then crosses the elbow joint anterior to the lateral epicondyle of the humerus. At the elbow the radial nerve divides into a motor nerve, the posterior interosseus nerve; and a sensory nerve, the superficial radial nerve.

Posterior Interosseus Nerve
The posterior interosseus nerve enters and innervates the supinator (Sup) muscle. The nerve then gives motor branches to - extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and extensor indicis proprius (EIP).

Superficial Radial Nerve (SRN)
At the elbow, the superficial radial nerve stays superficial to the supinator and proceeds anterolaterally, deep to the BR muscle. Approximately at the junction of the proximal two thirds and the distal one third of the forearm (approx 8 cm from tip of radial styloid), the SRN becomes superficial and crosses over to the posterior aspect of the distal radial forearm, passing superficial to the tendons of the anatomical snuffbox (APL, EPL, and EPB) and traversing the wrist over the extensor retinaculum. It supplies cutaneous sensation to the dorsal surface of the lateral hand, as shown in the figure.

Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition
2. Preston DC. Distal Median Neuropathies. In: Entrapment and other focal neuropathies; Neurologic Clinics: WB Saunders company, August 1999
3. http://www.wheelessonline.com/ortho/the_superficial_branch_of_the_radial_nerve_an_anatomic_study_with_surgical_implications