Global warming, bad for MS patients!


Wilhelm Uhthoff (1853-1927) a German neuro-ophthalmologist described an optic neuritis patient in 1890 who would develop episodes of temporary vision loss during physical exercise.

This condition, subsequently known as Uhthoff’s phenomenon, was later found to be caused by a rise in body temperature.

More than half of all multiple sclerosis (MS) patients spontaneously report being sensitive to environmental heat.

When specifically asked, as many as 70% MS patients report that high temperatures worsened their MS.


Increased temperature blocks action potentials in compromised (demyelinated) neurons resulting in slower conduction velocities and/or temporary failure of conduction altogether (conduction block).

This explains the temporary exacerbations in neurologic dysfunction that underlie Uhthoff’s phenomenon.

So what can you do?


Drugs like Ampyra (dalfampridine or 4-aminopyridine) improve conduction across demyelinated neurons, and can improve Uhthoff’s phenomenon, but these drugs are not currently FDA approved for this indication, and used off label can cost as much as $1200/month.  It might be cheaper to move to Alaska or buy a window box AC unit?

Post-operative peripheral neuropathy


Post provided by Kevin Turezyn, Drexel University College of Medicine Class of 2013:


While the overall risks of undergoing a procedure involving general anesthesia have decreased dramatically over the last 25 years, there is one phenomenon that still puzzles both anesthesiologists and surgeons: post-operative peripheral neuropathies.

Why a patient undergoing an appendectomy would wake up with weakness in their arm is still in large part a mystery. Luckily most patients recover fully, but a small subset suffer from permanent damage.

While relatively infrequent, peripheral nerve injury after anesthesia is one of the largest sources of professional liability for anesthesiologists. Estimates of its frequency range from .03% to .11% of patients who undergo anesthesia.

Interestingly, despite numerous attempts to decrease its incidence, anesthesiologists have had little success.

While the exact cause is unknown, many believe that it relates to patient positioning. There are several points in the body where nerves run very close to the surface leaving them vulnerable to injury. For example, the most commonly injured nerve is the Ulnar nerve of the arm. When this nerve goes through the elbow, it is very close to the surface where it has little body tissue for protection. People commonly hit this nerve in daily life, giving them a painful sensation called hitting your “funny bone”. Other commonly injured nerves include the radial nerve (compression in the spiral groove against the humerus), brachial plexus from traction on the arm, sciatic nerve in the buttock and peroneal nerve against the fibula head.

The American Society of Anesthesiologists has published guidelines for prevention of perioperative peripheral neuropathies. The guidelines focus on pre-operative assessment for patients who are at higher risk ( diabetics, alcoholics, patients with peripheral vascular disease) as well as proper positioning of the extremities and adequate padding.

Click here for the full guidelines.


When peripheral nerve injury does occur, it frequently resolves on its own, although this can take take several months. During this time, there is little that can done to speed recovery. Physical therapy is often recommended to prevent muscle contractures and atrophy during this time period.

If a patient feels that they suffered a nerve injury during surgery, it is important that they be evaluated right away by a trained neurologist. Testing such as an electromyogram (EMG) can be done to determine the location of the injury and prognosis for recovery.

cts emg

Feeling sunburnt in winter? It could be small fiber neuropathy.



Nerves are composed of bundles of individual fibers (axons)


Nerve fibers (axons) come in a variety of shapes and sizes.  Some are wrapped in insulation (myelinated) others are bare (unmyelinated).

Human nerve

You can see from the figure (above) that small unmyelinated fibers make up the majority of human sensory nerves.  These small unmyelinated fibers convey pain and temperature sensitivity.


Small fiber neuropathy

Some diseases, particularly diabetes, preferentially affect these small unmyelinated fibers, leaving the other fibers relatively unaffected, resulting in small fiber neuropathy.

Symptoms of small fiber neuropathy are usually a mixture of numbness (sensory loss) and neuropathic pain.

The pain can be superficial and burning, deep aching, pins-and-needles, electrical shocks, or knife-like stabbing.  Innocuous contact (such as with clothing or bedclothes) can become painful like a sunburn.

Small fiber symptoms often worsen at night (when there are fewer distractions) and in the cold.

The symptoms usually begin in the feet, often first affecting the toes and/or soles.  As the condition worsens, the symptoms usually spread proximally up on to the legs and ultimately on to the hands, leading to a “glove and stocking” pattern.

Peripheral Neuropathy, Length Dependent

In most neuropathies, the ends of longest nerves are affected first (left), leading to a glove and stocking distribution of pain and numbness (right).


Autonomic dysfunction from small fiber neuropathy can cause burning redness in the feet (“erythromelagia”):



Also, loss of innervation to the sweat glands can cause decreased sweating peripherally (where the neuropathy is worse), and lead to increased sweating on the head and trunk:

sweat test

Sweat test showing decreased sweating in t extremities (yellow) and increased sweating on the head and trunk (purple).


A Diagnostic Challenge!

It is the large myelinated fibers which sub-serve strength and deep tendon reflexes.  Furthermore, it it these same large myelinated fibers which are tested during a conventional nerve conduction study.

So the physical signs and electrophysiologic findings we typically rely on to diagnose neuropathy may be absent in small fiber neuropathy.

The most widely available diagnostic test is the punch skin biopsy to quantify epidermal innervation.

skin biopsy neuropathy

Skin biopsies, showing normal epidermal innervation (left) and epidermal denervation in small fiber neuropathy (right).


Managing Small Fiber Neuropathy

So, you know you have sunburn from small fiber neuropathy, now what?

The most important first step is to look for an underlying (treatable) cause, particularly occult diabetes, with blood work that includes a glucose tolerance test.  In the case of diabetes, monitoring and controlling the blood glucose, is the most important next step.

Otherwise, treatment is usually limited to symptomatic measures, using drugs like gabapentin, pregabalin and/or duloxetine.

Parsonage-Turner Syndrome

shoulder pain
Case Report and discussion prepared by Sidra Ghafoor, Drexel University College of Medicine Class of 2013.

Case: 65 yr old male presents with painful weakness, wating and tingling in the right arm.

When did it all begin? Three months ago patient experienced sudden onset severe pain down his neck accompanied by a tingling sensation in his right forearm and thumb. There was no apparent cause for his symptoms (i.e. no trauma). After 3-4 weeks, his pain miraculously disappeared! Unfortunately, once the pain subsided, he began experiencing weakness in the right shoulder/upper arm and right hand.

Physical Exam (*all findings pertain to patient’s right side*)

  • Muscle Bulk/Tone: Atrophy of supraspinatous, infraspinatus, deltoid, and biceps          
  • Muscle Strength
    • Weakness of supraspinatus, infraspinatus, biceps, brachioradialis, and pronator teres
    • Normal strength of Rhomboids, trceps, wrist and hand muscles    
  • Sensation: Numbness over lateral arm, forearm, and anatomic snuffbox             
  • Reflexes: Absent biceps and brachioradialis

Parsonage-Turner Syndrome (Neuralgic Amyotrophy, Brachial Neuritis)

    • Incidence: relatively rare (1-2 cases per 100,000)
    • Sex/Age
    • Cause: unknown etiology – but linked to recent illness/events:
    • Clinical Correlation
      • Affects Lower Motor Neurons of brachial plexus and/or individual nerves or nerve branches (this explains the patchy clinical findings on exam).  The suprascapular nerve long thoracic nerve, phrenic nerve, and branches of the median nerve are nearly always affected:
Brachial neuritis, wasting of the shoulder girdle muscles

Brachial neuritis, wasting of the shoulder girdle muscles innervated by the suprascapular nerve.

Brachial neuritis, winged scapula

Brachial neuritis, winged scapula from involvement of the long thoracic nerve

Brachial neuritis, elevated hemidiaphragm from involvement of the phrenic nevre

Brachial neuritis, elevated hemidiaphragm from involvement of the phrenic nerve

  • Clinical Sequence of Events
    • (1) Acute onset severe unilateral pain (throbbing, aching) in shoulder/arm
    • (2) Pain resolves within 1-3 weeks
    • (3) weakness/wasting of involved muscles and variable sensory impairment
  • Prognosis
    • Full recovery in majority of cases by 6 months to 1 year
    • Rarely recurrent (exception: familial neuralgic amyotrophy is typically recurrent)
  • Diagnosis
    • Clinical Clues: acute onset, pain followed by weakness & impaired sensation, no preceding trauma
      • aggravated by movement but not by coughing, sneezing, laughing (this helps to differentiate it from Cervical Radiculopathy in which pain is aggravated by coughing/sneezing/laughing)
    • Physical Exam Clues: patchy involvement of nerves
      • affected arm is internally rotated and adducted at shoulder.  flexed at elbow.
    • EMG: localizes lesion to brachial plexus and differentiates it from Peripheral Focal Neuropathy and Cervical Radiculopathy
      • 1 wk after onset: Loss of sensory and motor amplitudes with relatively normal conduction velocity
      • 2-3 wks after onset: shows denervation (fibrillations, positive sharp waves, and/or motor unit potential changes) in affected muscles
  • Management

The Importance of Correct Positioning During Anesthesia

This post is provided courtesy of K. T. Weber, Drexel University College of Medicine Class of 2013:

When a patient goes under anesthesia, a highly trained team of people take over and monitor the body. This team controls breathing, circulation and many other processes, filling in very well for the patient’s brain… however, there is one function that cannot be replicated by the anesthesia team: movement. In order to undergo surgery, a patient must have their muscles relaxed, and therefore will not move away from sore or painful spots. It is normal for people to fidget, rearranging their weight to more comfortable positions, which helps to prevent bed sores (decubitus ulcers) as well as preventing minor nerve compression.

Decubitus (Pressure) Ulcer

Decubitus (Pressure) Ulcer

Decubitus (or “pressure”) ulcers can be a devastating complication for patients who undergo very prolonged surgeries – Superman actor Christopher Reeve actually died from complications associated with an infected pressure ulcer. Fortunately, these wounds are very rare in patients who are only temporarily relaxed for surgery, and there are many precautions in place to prevent this from occurring.


Nerve Injury

However, minor nerve injury is still possible! One of the less commonly discussed side effects of having surgery, this minor nerve injury can be very disconcerting and affects a surprisingly large number of people

Nerve damage can occur in several forms based on the type and cause of injury:

The mildest form of nerve injury is neurapraxia, where the myelin sheath and support cells around the nerve are damaged (frequently by excessive pressure or ischemia), leading to poor signal conduction along an otherwise unharmed nerve. Neurapraxia improves on it’s own with time as the myelin sheath regenerates, and does not directly involve injury to the axon of the nerve.


Neurotmesis, the most severe type of injury, occurs when a nerve is lacerated, over-stretched or very badly crushed, and the two ends of nerve are actually separated from each other.  These nerve injuries will not get better on their own without nerve graft repair surgery.

Untitled-1 copy

Axonotmesis is an intermediate type of nerve injury, where the nerve is damaged (often by crushing) but the support cells around the nerve are intact and aid regeneration, so (slow) spontaneous recovery is possible.

The most common symptom of compressive nerve injury is numbness or pain. The tingling, pins-and-needles feeling of hitting one’s funny bone is a classic example of nerve pain.  Many patients who have undergone surgery and are held in one position for an extended period of time may wake up with areas on their skin that feel extra sensitive, like a sunburn. It is understandable to be concerned by waking up with hyperaesthesia, or pain in response to something that wouldn’t normally be painful! Weakness and uncoordination is less common, and only occurs after more severe or prolonged nerve compression during surgery.

The good news for patients who wake up with an unusually sensitive area or some numbness after having surgery is that this minor nerve damage tends to improve rapidly. Neurapraxia resolves as the swelling and bruise around the nerve decreases and the cells that help conduction recover, sometimes as quickly as a few hours, sometimes as slowly as several months. If necessary, non-steroidal anti-inflammatories, other medications for neuropathic pain and splinting can help treat the symptoms of mild nerve damage. Even more severe forms of nerve  injury can recover with time – peripheral nerves grow back around 1mm per day! In the most extreme cases, without the potential to regenerate on their own with time, nerve graft repair can be discussed as an option.

Watch a video presentation on nerve injury and repair:

Of course, an ounce of prevention is worth a pound of cure. The skilled members of the operating room staff take extensive measures to protect their patients with adequate padding and careful positioning.