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Your mother is 49 years and having spasmodic pelvic pain, it is good that she is not having any stone in kidney or ureters.
There are many diseases which can cause pelvic pain, common possibilities include Pelvic inflammatory disease
, Endometriosis, Bladder pain Interstitial cystitis
, UTI Chlamydia Infection
, Pelvic congestion syndrome
and even Uterine Fibroids and Malignancy.
She may need further investigations to detect the cause and treatment depends on cause.
She may require a urine culture,endometrial biopsy, tests for chlamydia, and CT scan or MRI study.
Hope this is useful for you.
Dr.Akhilesh Dubey M.D.