Q. Why is my left leg thinner than my right leg?

Answered by
Dr. Hitesh Kumar
and medically reviewed by Dr. Chithranjali Ravichandran
This is a premium question & answer published on Apr 26, 2021

Hello doctor,

I have a question regarding atrophy in my thigh. I have some herniated disks at L3/4, L4/5, and S1 and also spinal stenosis on those disks. The EMG only found problems on my left calf, but not on my thigh. Do you have any idea where this atrophy can result from? My left leg always has been weaker than the right. I did not realize it because of weakness, only because of getting smaller.



Welcome to

I would like to know some details about your symptoms:

1. Since when your symptoms started? Please tell sequentially.

2. Symptoms started with back pain? Or you noticed thinning of the left leg first?

3. Do you have any weakness in the left leg? If yes, what activity of the left leg is limited?

4. Do you have any pain in the legs (coming down from the back)? If yes, which leg and parts?

5. Do you have any tingling sensation in the legs? If yes, which leg and which part of the leg?

6. Do you have any other medical history - like diabetes or blood pressure or any other significant medical problem? Are you taking any medications (if yes, please mention medicines names with dosage and frequency)

7. Which area of the left leg look thin (compared to right)? If possible, please send pictures of the area showing thinning with the right leg alone with (for comparison)

8. Have you consulted a neurologist physically? I would like to get your physical assessment sheet to know which muscles of the leg how much power and how are deep tendon reflexes in the hands and legs?

Treatment plan:

Your nerve conduction study is showing less conduction velocity of a motor nerve in both legs and EMG showing denervation changes in leg leg calf area muscles.
Such changes can happen due to involvement of their nerves within leg or at their origin in spinal cord and rarely due to involvement of the origin cell (motor neuron).

Regarding follow up:

Please revert with above mentioned information for better understanding and further decision making.
Along with please send (As attachment):
- photographs showing atrophy in left leg (while keeping right leg sideways).
Neurologist/ physiotherapist assessment sheet.
Your MRI spine images via CD - upload it in icliniq DICOM viewer and its reports.
Other reports.

Hello doctor,

I am still waiting for my new MRI report. My problem started in early February with severe pain in my left thigh and pain coming from my lower back. The pain in my thigh was worse than the pain from my lower back. That is why I checked my legs and realized the difference. I also had pain in my left butt. I realized first my right leg and thought this one got bigger, but my physical therapist told me that the left leg got smaller because of muscle atrophy. My left leg was always weaker due to knee surgery a few years back. I know that these parts of my knee were the same because I had liposuction on both, six years back. There were very defined. That is why I first realized my right knee. I have no weakness in the leg and can do everything I want. I have scoliosis, and my left leg is shorter than the right. I had to sit most of the days. I have no tingling sensation, and my pain sometimes runs through in left butt towards my leg. My pain management specialist gave me an injection in L4/L5 and L5/S1. Afterward, the pain in my left thigh has been 98% gone, and the lower back pain on the left side also. I still feel a bit through my butt till my feet. My physical therapist said that my strength in both legs is fine. I made a mistake and checked online, and that is why I am scared of having something like ALS now.



Welcome back to

As per your description, there may be two possibilities or a combination of both:

1. With a background of having scoliosis with a short left leg, there is the possibility of developing some thinning of leg in a shorter leg.

2. Lower back pain radiating to left butt and leg raises a possibility of some nerve root compression, maybe some protruded disc in the lumbosacral spine. (As you mentioned, your previous MRI spine showed a herniated disc at L3-L4, L4-L5 & S1 level). Prolonged severe nerve root compression can also lead to some atrophy of its innervated muscle.

Scoliosis patients are more prone to develop disc problems in the spine.

Treatment plan:

Atrophy of muscle is in the same distribution which has shorter leg length and also have radicular pain. So with this clinical scenario, there is likely possibility that cause of this muscle atrophy can be due to these factors.
Possibility of ALS seem unlikely.
But there is no full proof way to say that it cannot be ALS, as it will be known with time only. There is no test available which can rule out ALS.
ALS is more of a clinical diagnosis and can be made only if it fulfills the diagnostic criteria, requiring signs and symptoms in different nerve root segments of body and if no other cause explaining those symptoms or sign is found.
But your symptoms and sign (clinical +electrophysiological) are limited to only one segment (lumbosacral) till now and are explainable by short leg and lumbar disc problem.

If there be found severe nerve compression by disc bulges, atrophy in innervated muscles may be indication to consider surgical treatment of disc bulges along with medical management.
Also need to do regular physiotherapy (to prevent or slow down further atrophy) - only under guidance of physiotherapist.

Regarding follow up:

Revert with MRI images (upload via DICOM viewer in icliniq) and report along with the neurologist/ physiotherapist assessment sheets.

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