Lower back pain is typically not a cause for serious alarm, but if you experience the following two symptoms related to lower back pain you should seek immediate medical attention:
See Getting an Accurate Back Pain Diagnosis
1. Progressive leg weakness
Progressive weakness in your lower extremities (legs and/or feet) may be a symptom of cauda equina syndrome (you may also feel weakness in your hips, genital area, and buttocks). Cauda equina syndrome is usually caused by an injury to your spine, a spinal condition, or an infection that results in the severe compression of your entire nerve sac in your lumbar spine.
The name cauda equina comes from the Latin for "horse’s tail," as the nerves at the end of your spine share a resemblance with a horse’s tail.
Treatment for cauda equina syndrome typically entails immediate surgical decompression to reduce or eliminate the pressure on your affected nerves. If left untreated for too long, cauda equina syndrome may lead to paralysis, loss of sensation below your lumbar spine, and a loss of bladder and/or bowel control.
2. Acute back pain with abdominal pain
If you experience the sudden onset of lower back pain that is not clearly connected with an injury or other cause, you may be suffering from an abdominal aortic aneurysm.
The aorta is your body’s main artery, and it stretches from your heart all the way through your abdomen. As a general rule, if an abdominal aortic aneurysm results in severe abdominal and/or back pain it is considered life-threatening, as it likely indicates a rupture. Other life-threatening indicators may include symptoms of shock as well as low blood pressure.
If your abdominal aortic aneurysm is not detected until it reaches the point of an emergency, you will likely need immediate surgery to repair your ruptured artery.
The above list is not comprehensive, as other symptoms like unexplained fever and bowel and/or bladder incontinence also require immediate medical attention. But the bottom line is that it is better to be overly cautious when it comes to addressing potentially dangerous lower back pain symptoms. So when in doubt, seek medical care.