discogenic

Determining a Painful Disc | Authors propose sub-type diagnosis

The intervertebral disc, a key structure in the human spine, is a significant source of low back pain. However, the concept of discogenic pain has yet to be widely accepted, leading to confusion among physicians and patients. This lack of clarity has implications for health information management, as there are no ICD-10-CM coding sub-terms for “discogenic” back pain.1

Chronic low back pain is a common issue, with various sources having well-defined ICD-10-CM codes. However, discogenic pain lacks a corresponding code, limiting the accuracy of coding practices and data quality. Most patients recover with time and conservative care, but 5% of patients experience chronic, severe pain and functional impairment, which consumes most healthcare costs. Intractable, discogenic pain accounts for around 40% of patients with chronic low back pain. This article aims to provide a perspective and rationale for creating specific ICD-10-CM codes to describe, characterize, and define pain associated with lumbar and lumbosacral degenerative disc disease, developed under the aegis of the International Society for the Advancement of Spine Surgery (ISASS) with the endorsement of the American Academy of Orthopaedic Surgeons (AAOS) and American Association of Neurological Surgeons (AANS).

discogenic
A C4-7 cervical model with hypermobile and inflamed C5-6 disc

Pathophysiology

The intervertebral disc is a crucial structural element in the spine, serving as a load transfer junction and supporting the normal spine’s three-dimensional kinematics. Its unique morphology and structure reflect its functions. In healthy discs, it has substantial load-bearing capacity and inhibits nerve and vascular ingrowth. However, degeneration of the lumbar intervertebral disc precedes all other connective tissues in the human body. As degeneration progresses, the disc becomes less efficient in absorbing physiological loads, leading to abnormal load transfer to adjacent vertebral bodies and facet joints.

The intervertebral disc can cause pain and reduce the quality of life for millions of patients worldwide. Pathologic internal disc disruption, characterized by nuclear matrix degradation and annular tears, is distinct from asymptomatic disc degeneration, a common aging phenomenon. Symptomatic disc degeneration is caused by repetitive mechanical loading, causing endplate microfractures and outer annular fibre disruption, leading to matrix damage, inflammation, sensitization, and hypermobility.

Internal disc disruption is a complex condition that can result in intractable lower back pain. Imaging evidence of disc disease often includes decreased disc signal and a high-intensity zone on T2-weighted magnetic resonance images. Anatomical changes include subchondral bone sclerosis, disc space narrowing or collapse, posterior annular tears, fissuring, ruptures, and delamination, which can ultimately result in intractable pain. Histological studies have shown that disc degeneration and lamellar disruption are associated with neovascularization, neuronal penetration with unmyelinated nerve fibres, and the ingrowth of Schwann cells.

Radial annular fissures induce nerve ingrowth into delaminated regions, while solitary concentric fissures involve torn collagen fibres that attract an inflammatory repair response. Radial fissures extend into the outer innervated third of the annulus and strongly correlate with the reproduction of the patient’s pain by discography. These fissures are mechanically and chemically conducive to the ingrowth of nerves and blood vessels by providing a low-pressure microenvironment that facilitates focal proteoglycan loss, leaving a matrix receptive to nerve and blood vessel ingrowth. Painful discs result from a repetitive cycle of injury and repair, with vascularized granulation tissue embedded along torn annular fissures.

The ingrowth of nerve endings serves as the pathoanatomic correlate to the dull chronic ache experienced by patients with chronic low back pain, often referred to as discogenic pain. The likelihood of a concentric or circumferential tear of the posterior or posterolateral annulus is increased if axial rotation occurs in combination with flexion. Patients with definitive imaging evidence of internal disc disruption have a poor prognosis for recovery with conservative management alone, potentially leading to opioid dependency or major surgery.

annular tear and back pain model
Professional LxH Dynamic Disc Model

How does it present clinically?

• Characterized by axial midline low back pain, sitting intolerance, and pain with flexion.

• Pain is described as dull, aching, and gnawing.

• Can be coupled with referred pain to the lower extremities, usually above the knees.

• Discogenic pain involving the legs is somatic and sclerotomal, expanding into broad areas.

• Patients can confidently identify its center or core.

• No neurological radicular signs as somatic referred pain is not caused by nerve root compression.

Clinical examinations for low back pain related to disc herniation or spinal stenosis with radiculopathy differ from those associated with neuro-compressive disorders. Identified physical signs include positive leg raise, Lasegue’s sign, crossed Lasegue’s sign, positive bowstring, positive femoral stretch tests, motor/sensory/reflex changes, and electromyography changes. Lower extremity radicular pain is typically electric and shocking.

 

Diagnosis – How?

Discography is a minimally invasive diagnostic test used to confirm the diagnosis of disc degeneration associated with chronically severe discogenic pain. Developed in the 1950s, it is often performed provocatively via intradiscal injection of contrast agents or using a small dose of anesthetic agent to relieve pain. This test is essential before intradiscal treatments and has been used for decades to differentiate discogenic pain from other pain generators. Provocative discography is often combined with computed tomography to identify the location and extent of annular disruption. Recent advancements have shown that a specialized magnetic resonance spectroscopy exam can identify chemically painful lumbar discs and improve patient-reported outcomes following surgery for discogenic low back pain.

Author’s Proposal:

The ISASS proposal, supported by AAOS and AANS, aims to create new ICD-10-CM diagnosis codes for pain associated with lumbar and lumbosacral degenerative disc disease or lumbar “discogenic” disease. Currently, there is no specific code to classify and define discogenic pain, unlike other chronic low back pain sources. The proposal proposes modernized ICD-10-CM codes that define pain associated with lumbar and lumbosacral degenerative disc disease, allowing pain to be characterized by location. This would improve coding precision and improve clinical assessment, diagnosis, and treatment strategies.

Conclusion

Chronic low back pain is a common cause of pain, but the current diagnostic labels lack specificity and clarity for lumbar degenerative disc disease. This is due to the lack of specific ICD-10-CM codes for pain of discogenic origin. The existing ICD-10-CM terminology needs to be more specific and updated for lumbar disc degeneration, leading to under-reporting cases. Recently, vertebrogenic pain was granted a specific ICD-10-CM diagnostic code (M54.51), which can be applied to patients receiving basivertebral nerve radiofrequency neurotomy treatment. The new code for vertebrogenic pain, “pain coming from endplate bone,” couples symptoms with the etiology, and the association between lumbar disc degeneration and chronic low back pain warrants similar coding schema for “pain coming from the disc.”