Brief Answer:
Compression of nerve and blood vessel suspected

Detailed Answer:
Hello XXXXXXX

Thanks for your query.

Regarding the symptoms as mentioned in your post, kindly let us know about the following:
1. Any recent illness or injury to the back or lower limbs?
2. Sensation of radiating pain and mottling of skin can be due to vasculopathy or neuropathy secondary to systemic illness. Is there is significant past history or family history of systemic disease like Diabetes, Hypertension, Thyroid disorder, etc. ?
3. Any recent history of Stress, improper nutrition & lack of sleep?
4. Habit of smoking or alcohol consumption?
5. History of prolonged intake of any medication?
6. Any other associated symptoms?

If your answers to the above mentioned questions are "NO" then the symptoms can be attributed to:
1. Compression of nerve and blood vessels (as suspected by you) at the Lumbosacral region: the sensation of pain radiating from buttock fold down to knees can be explained on the basis of it. The fact that she is a nurse and works on her feet for most of her working hours acts as a risk factor.
2. Inadequate hydration status & electrolyte imbalance of the body, or
3. Dietary deficiencies of certain nutrients like Iron, Calcium, Vitamin D, Vitamin B12, Folic acid, etc. which help in blood formation & nerve conduction.

Though analgesics and heating pad will provide temporary relief, the underlying cause needs to be treated.
Symptomatic relief can be obtained by intake of nervigenic agents (like Vitamin B6, Vitamin B12, Folic acid) as well as multivitamin & multimineral supplements including iron, calcium & Vitamin D needs to be added in her diet.
Physiotherapy & postural spinal exercise will be helpful.
Also make sure that your sister avoids lifting of heavy weights or twisting of her back.

If symptoms still persist, kindly consult a Neurologist & get a complete Neurological examination done.
Certain investigations like complete blood count, serum electrolyte estimation, fresh estimation of blood pressure & blood sugar levels, nerve conduction studies, Ultrasound scan of abdomen & pelvis and Doppler study of lower limbs will be helpful to rule out any pathological cause for the symptoms.
X ray & MRI of Lumbo-sacral spine can also be carried out to detect any nerve entrapment.

Wishing her a Good Health.
Please let me know if I need to clarify further.
Take care.

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