P Vinci counters Van Pomeren about the hypothesis of overwork weakness in CMT

[Guest guest]

J Rehabil Med 2009; 41: 778–779

Letter to the editor

ABOUT THE HYPOTHESIS OF OVERWORK WEAKNESS IN CHARCOT-MARIE-

TOOTH DISEASE

Sir,

We read with interest the recently published article by Van

Pomeren and colleagues (1), describing their study of 28

patients with Charcot-Marie-Tooth disease (CMT), which

aimed to verify our hypothesis (2) of overwork weakness (OW)

in this neuromuscular disorder.

They found equal muscle strength in the dominant and non-

dominant hands, rather than more strength in the non-dominant

hand, and they therefore questioned the occurrence of OW in

CMT and suggested that the patients’ activities should not be

limited. However, we are of the opinion that their results differ

from ours because their sample differed from ours, and that

their patients have undergone OW.

Our study was conducted on a large sample of patients

(n = 106) with all degrees of muscle impairment, whereas

the study by Van Pomeren et al. considered only 28 patients

with far milder hand involvement (our 25th percentile for

the dominant abductor pollicis brevis muscle was Medical

Research Council (MRC) grade 0, whereas theirs was MRC = 4

in CMT type 1 and MRC = 3 in type 2). If only a few nerve

fibres have undergone axonal degeneration, overloading has

little chance to act because there are enough remaining motor

units to alternate, even in the case of movements requiring

quite a high level of muscle power. On the contrary, if only

a few axons have survived and have undergone sprouting to

compensate for the loss of other nerve fibres, they are more

susceptible to possible deleterious effects of intense physiological

stimulation because all the motor units must always

be activated; in addition, muscle fibres that have undergone

compensative hypertrophy might split and degenerate in cases

of overuse, as happens in post-polio syndrome.

The fact that both sides showed the same strength, rather

than greater strength in the dominant side, as is seen in most

normal subjects due to muscle hypertrophy in muscles that are

used more (2–4), suggests that the OW phenomenon is also

present in the patients tested by van Pomeren et al.: if it was

not so severe as to cause more weakness in the dominant hand

than in the non-dominant hand, this may have been due to the

mildness of the neuropathy in their cases. Also, in our study

approximately one in 3 hands showed equal strength, and this

figure would be higher if only the muscles at MRC = 5 and 4

were considered.

In questioning the occurrence of OW in CMT, van Pomeren

et al. also cite the results of a study by et al. (3), who

found equal grip and pinch strength in both hands of their

patients. Apart from the fact that grip and pinch strength is

generated not only by the intrinsic hand muscles selectively

involved by the neuropathy, but also by relatively unaffected

forearm muscles that can undergo hypertrophy as in healthy

subjects, et al. (3) found that, in controls, the dominant

hand was stronger than the non-dominant hand, which suggests

that some OW had also occurred in their patients.

Van Pomeren et al. also cited 2 clinical trials (5, 6) on limb

strength training to support their hypothesis of no risk of OW in

CMT. In both of these studies the resistance exercises included

only proximal muscles (hip, knee and elbow activators), which

are relatively spared by the disease (7), maximal resistance was

never used, and the sessions and the training period were short,

which may be why these exercises were not harmful.

On the contrary, prolonged maximal contraction of the

distal muscles, the axons of which are selectively involved in

a length-dependent neuropathy such as CMT, as required by

some occupational activities or compensations, can result, in

time, in permanent damage, as we have observed in numerous

patients after long periods of intense handwriting or using a

computer mouse (8–9).

To conclude, despite the fact that a direct demonstration of

OW cannot be given, because a study of OW using exercise

against maximal resistance would be unethical as it may lead to

permanent loss of muscle strength, there is sufficient evidence

that OW also occurs in CMT.

We therefore conclude that it is appropriate to advise patients,

especially if their form of CMT is not mild, about the

proper use of their strength and about surgical or orthotic

measures (8, 9) to maintain an active life without accelerating

neuromuscular deterioration.

Paolo Vinci, MD1*, Linet Perelli, MD2 and

Paola Gargiulo, MSc1

From the 1Service of Rehabilitation, Italian Charcot-Marie-

Tooth Association (AICMT-Onlus), Via dei Castelli Romani 6,

00040 Rocca di Papa and 2Unit of Rehabilitation, San Camillo-

Forlanini Hospital, Rome, Italy.

J Rehabil Med 41 © 2009 The Authors. doi: 10.2340/16501977-0425

[Guest guest]

These finding mirror my experiences with my case. I can point to a number of

times that I have started activities and had to finish them despite muscle

spasms from overexertion, within a couple of weeks I notice more loss of

function.

Ed

[Guest guest]

I had to smile in agreement when I read this response to overwork weakness.

I can totally agree with over work of delicate tiny CmMT effected muscles.

I have learned to be careful during my time resting. Back when I was almost

totaling exhausted after a week of work and transporting kids, dinner etc.

I would be in bed basic for the weekend resting up to start the week again.

In this rest period if I did extensive typing on computer(like when I wrote

up a cliff notes version of Vinci's CMT book for my Drs)or used the mouse

for work all weekend I could not move my fingers. Then on Monday my

fingers were wiped out and I couldn't use my hands anymore.

Or if during a

PT evacuation or annual neuro visits the Dr would request me to stand on my

toes and lower my heels as many times as I could - and now I say I can do it

and I could do many but won't be able to walk tomorrow.

It is just that

realization that if I do 10 toe roles with a towel I may feel that pain for

5 days and that causes me to stop moving but I can do bigger movements and

be just fine. It is those big, unaffected muscle groups which we cannot

give up on.

This experience and better understanding of how specific the

effects of CMT can be has helped me see the bigger picture of health and given

me hope and the expectation that I will get back to being very active or at

least a whole lot more healthy again.

Kim

From: [mailto: ] On Behalf Of

gfijig

Sent: Friday, September 25, 2009 1:33 PM

Subject: P Vinci counters Van Pomeren about the hypothesis of

overwork weakness in CMT

J Rehabil Med 2009; 41: 778-779

Letter to the editor

ABOUT THE HYPOTHESIS OF OVERWORK WEAKNESS IN CHARCOT-MARIE-

TOOTH DISEASE

Sir,

We read with interest the recently published article by Van

Pomeren and colleagues (1), describing their study of 28

patients with Charcot-Marie-Tooth disease (CMT), which

aimed to verify our hypothesis (2) of overwork weakness (OW)

in this neuromuscular disorder.

They found equal muscle strength in the dominant and non-

dominant hands, rather than more strength in the non-dominant

hand, and they therefore questioned the occurrence of OW in

CMT and suggested that the patients' activities should not be

limited. However, we are of the opinion that their results differ

from ours because their sample differed from ours, and that

their patients have undergone OW.

Our study was conducted on a large sample of patients

(n = 106) with all degrees of muscle impairment, whereas

the study by Van Pomeren et al. considered only 28 patients

with far milder hand involvement (our 25th percentile for

the dominant abductor pollicis brevis muscle was Medical

Research Council (MRC) grade 0, whereas theirs was MRC = 4

in CMT type 1 and MRC = 3 in type 2). If only a few nerve

fibres have undergone axonal degeneration, overloading has

little chance to act because there are enough remaining motor

units to alternate, even in the case of movements requiring

quite a high level of muscle power. On the contrary, if only

a few axons have survived and have undergone sprouting to

compensate for the loss of other nerve fibres, they are more

susceptible to possible deleterious effects of intense physiological

stimulation because all the motor units must always

be activated; in addition, muscle fibres that have undergone

compensative hypertrophy might split and degenerate in cases

of overuse, as happens in post-polio syndrome.

The fact that both sides showed the same strength, rather

than greater strength in the dominant side, as is seen in most

normal subjects due to muscle hypertrophy in muscles that are

used more (2-4), suggests that the OW phenomenon is also

present in the patients tested by van Pomeren et al.: if it was

not so severe as to cause more weakness in the dominant hand

than in the non-dominant hand, this may have been due to the

mildness of the neuropathy in their cases. Also, in our study

approximately one in 3 hands showed equal strength, and this

figure would be higher if only the muscles at MRC = 5 and 4

were considered.

In questioning the occurrence of OW in CMT, van Pomeren

et al. also cite the results of a study by et al. (3), who

found equal grip and pinch strength in both hands of their

patients. Apart from the fact that grip and pinch strength is

generated not only by the intrinsic hand muscles selectively

involved by the neuropathy, but also by relatively unaffected

forearm muscles that can undergo hypertrophy as in healthy

subjects, et al. (3) found that, in controls, the dominant

hand was stronger than the non-dominant hand, which suggests

that some OW had also occurred in their patients.

Van Pomeren et al. also cited 2 clinical trials (5, 6) on limb

strength training to support their hypothesis of no risk of OW in

CMT. In both of these studies the resistance exercises included

only proximal muscles (hip, knee and elbow activators), which

are relatively spared by the disease (7), maximal resistance was

never used, and the sessions and the training period were short,

which may be why these exercises were not harmful.

On the contrary, prolonged maximal contraction of the

distal muscles, the axons of which are selectively involved in

a length-dependent neuropathy such as CMT, as required by

some occupational activities or compensations, can result, in

time, in permanent damage, as we have observed in numerous

patients after long periods of intense handwriting or using a

computer mouse (8-9).

To conclude, despite the fact that a direct demonstration of

OW cannot be given, because a study of OW using exercise

against maximal resistance would be unethical as it may lead to

permanent loss of muscle strength, there is sufficient evidence

that OW also occurs in CMT.

We therefore conclude that it is appropriate to advise patients,

especially if their form of CMT is not mild, about the

proper use of their strength and about surgical or orthotic

measures (8, 9) to maintain an active life without accelerating

neuromuscular deterioration.

Paolo Vinci, MD1*, Linet Perelli, MD2 and

Paola Gargiulo, MSc1

From the 1Service of Rehabilitation, Italian Charcot-Marie-

Tooth Association (AICMT-Onlus), Via dei Castelli Romani 6,

00040 Rocca di Papa and 2Unit of Rehabilitation, San Camillo-

Forlanini Hospital, Rome, Italy.

J Rehabil Med 41 C 2009 The Authors. doi: 10.2340/16501977-0425