The numbness in your lower limbs can be due to a couple of things. The first thing which comes to mind is that you could have a problem in the lower back which could be compressing the nerves. This would lead to numbness in the locations which you have mentioned as well as cause other symptoms like burning or tingling in some cases. This problem could be narrowing of the spinal canal or even a prolapsed disc. this would be diagnosed with a clinical examination and also with the help of a simple MRI of the lower back.
Another possibility of this numbness can be involvement of the peripheral nervous system. This means that the nerves of the lower limbs can be damaged because of several underlying issues which can include vitamin B12 deficiency, diabetes, autoimmune disorders, thyroid disorders, infections among many many other causes. This would cause numbness or even burning or tingling in the region. The diagnosis can be made with the help of a simple NCS/EMG test which would determine which nerves are damaged.
Another cause of this can be related to the brain, in some patients who have patchy numbness in various regions of the body along with other symptoms like muscle spasms or blurring of vision, that can be an indication of MS. However i dont think MS is the first thing i will think of here, this would be the LAST possibility i would keep in mind.
Lastly, simple electrolyte imbalances can also lead to this sort of numbness, particular with calcium, magnesium deficiencies. A simple blood test would be able to determine if this is the case,
Now i would suggest that you start with getting the back evaluated and also get a neurological examination. it is very likely that the numbness is the due to a problem in the spine or due to damage to the peripheral nerves.
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