Multifocal motor neuropathy

I am a 72 year old male with a neuropathy that started in 1996 with a weak left tricep.  Surgery removed bone spurs and fused C6 and C7.  There was some improvement but not 100%.

Since then there have been 3 occasions when weakness occurred:  twice in left hand and forearm, and once in right hand and forearm.  There is considerable muscle atrophy in both hands.

Neck MRI's and EMG and NCV tests indicate neck surgery would not help.  I have been told that it is not ALS or MS.

Extensive lab tests including metals and GMI antibodies were negative.
Acute intermittent porphyria was positive.
2005 EMG-NCV tests - Neurologist stated "no indication of conduction block to suggest Multi Focal Motor Neuropathy."
2008 EMG-NCV tests - A different Neurologist stated "no clear conduction block".  Possible etiologies include Multi Focal Motor Neuropathy, progressive muscular atrophy, or spine muscular athrophy".  This Neurologist suggests intravenous immunoglobulin might help.  These neurologists have different opinions --

1.  Can there be Multi Focal Motor Neuropathy without a conduction block?
2.  Should I proceed with the IVIG?

[Neuro Forum]

Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.

Without the ability to obtain a history and examine you, I can not tell you what your diagnosis is, nor can I comment on whether or not you should receive IVIG. However, I will try to provide you with information regarding multifocal motor neuropathy, which I will call MMN for short.

To put it simply, a motor neuropathy is a problem in the nerves that supply the muscles. MMN is a specific type of motor neuropathy. It often causes weakness in specific muscles in different areas of the body (as opposed to for example some motor neuropathies which cause weakness in most muscles in symmetric fashion i.e. on both the left and right side of the body, or other motor neuropathies which affect only one nerve).

In response to your first question, the answer is to a certain extent yes; there have been descriptions in the medical literature of MMN without conduction block. However, very few cases have been reported, and until more research is available, it can not be determined with certainty that the reports are not describing another condition all together with different causes and treatments.

I will explain to you what a conduction block is. A nerve consists of a cell body, you can think of it as sort of the brain of a cell, and a part called an axon, which you can think of as an arm or leg. The axon stretches out from the cell body and communicates with nearby cells. In order for an electric current generated by the cell to pass quickly to other cells, axons have a sheath of material around them called myelin. Myelin acts as an insulator, allowing electricity to flow fast along the axon to the next cell. In some conditions, such as MMN, there is damage to the myelin around the axon. The electric current moves slowly, and on an EMG/NCS, there appears to be a conduction block: a delay in the transmission of the electric impulse across the area that is lacking in myelin. In MMN due to demyelination, multiple conduction blocks are seen.

In rare instances, MMN, or an MMN-like condition, can be due a problem not in the myelin but in the axon itself, in which case conduction blocks will not be seen, but there will still be an abnormality in the transmission of the impulse on EMG/NCS.

Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck