About 60% to 90% of intervertebral disc herniation can be successfully treated with a conservative approach alone. The probability of spontaneous regression was 96% for disc sequestrations, 70% for extrusions, 41% for focal protrusions, and 13% for disc bulges. It is the fact that the higher grade of disc herniation type, the higher rate of spontaneous regression.
3 hypotheses have been proposed to explain the process of a herniated disc becomes smaller or disappears without surgical interventions.
(a) Retraction of herniated disc
The herniated disc could retract back into the intervertebral space which possibly happens with disc bulges and disc protrusions. However, it would be unlikely in cases of completely extruded or migrated fragments. This hypothesis was supported by an in vitro study by Scannell and McGill and was consistent with McKenzie’s theory (described as below).
Since extension of the lower back is the opposite movement of being hunched over, or flexed, it actually drives the pressure of the disc forward, creating a suction and can pull the disc material back into the intervertebral space.
(b) Dehydration of herniated disc
Disc regression is related to gradual dehydration and shrinkage within the nucleus pulposus leads to subsequent mechanical retraction of extruded material back into the annulus fibrosus, which correlates to the reports of higher MRI T2 signal intensity with higher regression rates.
(c) Inflammatory reaction and neovascularization
Extruded disc material into the epidural space of spine is recognized as a "foreign body" and induces an inflammatory reaction by the autoimmune system. This would result in neovascularization of the cartilaginous tissue along with infiltration by inflammatory cells, such as macrophages, granulocytes, and lymphocytes.
Spontaneous regression of a herniated disc may be related to retraction, dehydration and inflammation-mediated resorption. In conclusion, non-surgical interventions, for example physiotherapy can be considered as one of the treatment options when the radiculopathy (a condition due to a compressed nerve that causes pain) is acceptable and neurological deficit (altered function of body part such as muscle weakness) is absent.
References:
1. Chun-Chieh Chiu, Tai-Yuan Chuang, Kwang-Hwa Chang, Chien-Hua Wu, Po-Wei Lin and Wen-Yen Hsu. 2015. The Probability of Spontaneous Regression of Lumbar Herniated Disc: A Systematic Review. Clinical Rehabilitation 29(2): 184-195.
2. Xiaohui Yanga, Qin Zhanga, Xiaoning Haoa, Xinghua Guoa, Liping Wang. 2016. Spontaneous Regression of Herniated Lumbar Discs: Report of One Illustrative Case and Review of The Literature. Clinical Neurology and Neurosurgery 143: 86-89.
3. Sung-Joo Ryu and In Soo Kim. 2010. Spontaneous Regression of a Large Lumbar Disc Extrusion. J Korean Neurosurg Soc 48(3): 285–287.