Normal F Responses

Normal F wave responses

These are examples of normal F-wave responses from 73 healthy individuals.


Nerve      Site        value (msec)

Median    wrist      28

Ulnar       wrist      29

Peroneal  ankle     54

Tibial       ankle     55



Alavian-Ghavanini MR and Haqhpanah S.

Electromyogr Clin Neurophysiol 2000 Sept 40(6): 375-9

PFO and Stroke

PFO and stroke

PFO is a patent foramen ovale, a small hole connecting the atria chambers of the heart.  A PFO is found in about 25% of people.

Many cases of stroke are not explained, and are therefore labeled as cryptogenic stroke.  This means they are not found to be associated with narrowing of the cerebral arteries, abnormal heart rhythm, high cholesterol, smoking or high blood pressure.

It has been attractive to consider whether having a PFO increases the risk of stroke.  Perhaps a blood clot forms in a low flow vein, after a long plane trip.  It finds its way back to heart, with the other venous blood, then crosses the PFO, into the arterial system, and makes its way directly to the brain?  This mechanism of stroke is often speculated, but rarely proven.

Following most cases of stroke, patients are treated with antiplatelet medicines aspirin or Plavix to prevent a future stroke.  Studies have shown that patients treated with anticoagulation medicine or surgical PFO closure have not had better stroke prevention than patients treated with aspirin.  Although other studies are in progress, the results we have to date support the idea that most PFOs are not relevant to stroke risk.



Carroll JD et al.  RESPECT Investigators. Closure of patent foramen ovale versus medical therapy after cryptogenic stroke. N Engl J Med 2013;368:1092–1100.

Furlan AJ et al. CLOSURE I Investigators. Closure or medical therapy for cryptogenic stroke with patent foramen ovale. N Engl J Med 2012;366:991–999.

Homma S et al. ; PFO in Cryptogenic Stroke Study (PICSS) Investigators.Effect of medical treatment in stroke patients with patent foramen ovale: Patent Foramen Ovale in Cryptogenic Stroke Study.Circulation 2002;105:2625–2631.

Meier B et al.  PC Trial Investigators. Percutaneous closure of patent foramen ovale in cryptogenic embolism. N Engl J Med 2013;368:1083–1091

Shariat A et al. . Comparison of medical treatments in cryptogenic stroke patients with patent foramen ovale: a randomized clinical trial. J Res Med Sci 2013;18:94–98

Thoracic Outlet Syndrome

The thoracic outlet is a part of the body between the neck and the arm.  Three major structures pass through this – the nerves of the arm (the brachial plexus), the subclavian vein, and the subclavian artery.  Compression of the thoracic outlet structures often occurs by a muscle, muscular band or a cervical rib.  When any of these structures is compressed or squeezed, a person may develop symptoms of pain, color change, or numbness.  Sometimes these symptoms occur with specific arm positions.  This condition is known as thoracic outlet syndrome (or TOS).

Vascular thoracic outlet syndrome is a rare condition caused by compression of the subclavian artery or subclavian vein.  Sometimes these are referred to as arterial or venous TOS.  They may cause symptoms of swelling or bluish color change, pain in the fingers, coldness or pale coloration in the fingers, or poor oxygen supply to the fingers.  When compression of the vein or artery is confirmed, vascular surgery treatment is recommended.

Neurogenic thoracic outlet syndrome is a more common condition.  It may be related to a history of trauma or repetitive movement.  Symptoms of neurogenic TOS may include pain and weakness in the hand, pain in the neck or the back of the head, and tingling.  Coldness and color change may also occur, but this can be caused by nerve irritation rather than vascular changes.  No arm swelling or pulse changes are present with neurogenic TOS.

The symptoms of neurogenic thoracic outlet syndrome can sometimes be triggered by movement of the head or arms.  Rotating and tilting the head is one way to trigger the symptoms.  Another way is to raise the arms to the level of the shoulders , extend the wrists and tilt the head towards one side.  Sometimes this is a useful test during an office evaluation.  Congestion of veins on the chest or absence of a radial artery pulse with positioning of the arm is a helpful clue for vascular TOS.

Because TOS is affected by positioning of the arm, diagnostic testing for this can be misleading.  A chest xray will evaluate for the presence of an extra rib at the bottom of the neck.  The cervical rib is sometimes present at birth and it may influence symptoms of TOS.  In many patients, EMG or nerve conduction tests are normal.  The EMG is most helpful because it can assess for other conditions that mimic TOS.  MRI or MRA testing results can be variable, and often they are not helpful.

Treatment of TOS may benefit from physical therapy, medications, injection of anesthetic into a muscle that causes TOS, or sometimes surgery.  Surgery is rarely necessary for neurogenic TOS.

The following is a link to a thorough discussion of TOS, its diagnosis, and treatment at a TOS treatment center.

Screening for dementia

Do you know someone who might have dementia?

The diagnosis of dementia requires changes in cognitive function over several months or more.  People with dementia may lose interest in hobbies, be unable to complete complex tasks such as preparing food or lose track of important information such as appointments or due dates for bills.

Dementia is a medical condition diagnosed after a careful interview, a medical exam and medical tests.  There are several screening tests that are used to help decide if comprehensive testing is needed.

Some of these tests will evaluate:

  1. orientation.  Do you know what day it is?  What the date is?  What the year is?  Do you know what city you are in?  Do you know what street or floor you are on?
  2. short term memory.  Repeat the names of three words.  Recall them again after 1 minute.
  3. attention.  Count backwards from 20.  Spell a five letter word backwards.

The answers to these questions do not diagnose dementia, but if a person finds it hard to answer them, formal evaluation and treatment may be helpful.

Juvenile Myoclonic Epilepsy

Juvenile Myoclonic Epilepsy, or JME, is a generalized epilepsy that presents in adolescence.  It is a generalized epilepsy because the onset of seizures occurs throughout the surface of the brain.  This is indicated by abnormal discharges on EEG, often with strobe light stimulation.

JME often presents with episodic myoclonus, which are involuntary, brief muscle jerking symptoms.  These may be prominent in the morning.  Sometimes this causes small accidents, such as flinging a toothbrush or spoon, apparently by accident.  Patients with JME may also have absence seizures or generalized tonic clonic seizures, although these are less common.  Sleep deprivation may provoke seizures in JME.

People with JME have a risk of seizures throughout their life.  Neurologists recommend to continue treatment to prevent seizures indefinitely.

JME is a fairly common form of epilepsy, accounting for about 5-10 % of all epilepsy cases.

JME is often treated effectively with medication, especially valproate, levetiracetam or lamotrigine.