Symptomatic thoracic discogenic pain syndrome (TDPS) is a rare phenomenon making it challenging to diagnose. The rarity of TDPS is attributed to the particular orientation, structure, and function of the thoracic spine in the vertebral column. The thoracic spine and sacrum exhibit kyphosis which is present at birth, while the cervical and lumbar spine exhibit fully developed lordosis around puberty. The lordotic nature of the cervical and lumbar spine allows the imaginary line of gravity to run through, allowing them to bear most of the weight of the of the axial skeleton as compared to the thoracic and sacral spine. Consequently, they are subject to a higher percentage of degenerated discs and subsequent discogenic pain syndrome.
Between each vertebral body lies the intervertebral disc. The intervertebral disc is composed of two materials: the outer hard fibrous ring called the annulus fibrosis and an inner soft gelatinous core called the nucleus pulposus. The intervertebral disc functions to both absorb shock and allow flexibility of the vertebral column. As the body ages, the integrity of the intervertebral disc declines and causes the inner core of the disc to protrude through the outer layer. The effects of these will be either compression of the nerve roots or the spinal cord, giving rise to radicular or myelopathic symptoms.
The majority of the thoracic disc herniation is asymptomatic, or the patient presents with nonspecific symptoms like chest wall pain, epigastric pain, upper extremity pain, and sometimes, a pain in the groin or the lower extremity causing the clinician to think of a more common problem than a thoracic disc herniation. While the rare nature, coupled with the atypical presentation, may lead to delay in diagnosis, it has been significantly cited in the literature that MRI can be very useful in diagnosing thoracic disc herniations (TDHs). The majority of asymptomatic TDHs were often diagnosed due to incidental MRI findings. Treatment of thoracic discogenic pain syndrome is conservative but sometimes surgical. Surgical interventions, with surgical intervention associated with many complications.
Intervertebral disc degeneration primarily causes thoracic discogenic pain syndrome. The exact cause of disc degeneration is believed to be multifactorial. Factors that cause disc degeneration include trauma, metabolic abnormalities, genetic predisposition, vascular problems, and infections. Among these factors, trauma happens to be one of the most common causes of thoracic disc herniation. The effects of trauma as previously mentioned is less devasting on the thoracic spine as compared to the cervical and lumbar spine because the thoracic spine participates in less weight-bearing activities and the rib cage and coronal orientation of the facet joints make it more stable, hence less prone to degenerative disc disease. With trauma, chronic overload from the lifting of heavy objects or chronic multi-trauma from individuals participating in sports leads to the repeated rotation of the axial spine, causing vertebral instability with alteration of the of the spinal alignment that accelerates the risk of developing disc degeneration.
As mentioned above, thoracic disc herniation is rare and usually asymptomatic. It is found incidentally with MRI. Herniation of the intervertebral disc in the thoracic region makes up only 0.5% to 4.5% of all disc ruptures, 0.25-0.75 of all symptomatic disc herniation and 0.15% and 1.8% of all surgically-treated herniations. About 80% of patients usually present with problems in the third or fourth decades of life. About 75% incidence occurs below the T8 with a peak around the T11 to T12 and about 63% are symptomatic and have an incidence of one in one million.
Thoracic discogenic pain syndrome may be a radicular or myelopathic pain. The radicular pain is mostly secondary to posterolateral herniations that compress spinal nerves as they exit through the intervertebral foramen. Radicular pain will usually radiate towards the dermatome of the nerve roots innervated by the exiting nerve. Myelopathic pain, on the other hand, is seen in central herniations. In this case, the herniated disc compresses the spinal cord, leading to sensory and/or motor problems in the corresponding compressed area and below. This is particularly more severe in the thoracic spinal cord since the spinal canal in this region is smaller compared to the cervical and lumbar region. Hence, a slight compression will lead to symptoms. Majority of the thoracic disc herniation goes through a calcification process. While this calcification also causes symptoms, in some cases, the adherence of this calcified herniated disc to the dura may erode it, leading to a cerebrospinal fluid leak and patients presenting with atypical symptoms like a headache, orthostatic hypotension, and intracranial hypotension, a critical condition that requires immediate medical attention.
Nerve fibers that transmit both nociceptive and non-nociceptive information innervate the outer annulus of the intervertebral disc. Blood vessels that supply the outer annulus travel along with these nerve fibers. Pain from a herniated or degenerated of the intervertebral disc does not only occur from the mechanical compression of the spinal nerve root or spinal cord within the canal but also be secondary to inflammation of the nociceptive neurovascular supply of the intervertebral disc. Also noted, is the nerve growth factor-dependent neurons that play a role in the modulation of pain in response to inflammation of the intervertebral disc. The nerve growth factor-dependent neurons sensitize the dorsal root ganglion in response to inflammation of the intervertebral disc.
As mentioned early, the majority of the thoracic disc herniation are asymptomatic and are discovered incidentally with an MRI. Unlike the lumbar and cervical disc herniations, thoracic disc herniations have atypical symptoms and often a diagnosis of exclusion. To accurately diagnose thoracic discogenic pain syndrome, a thorough history and physical examination should be done. As part of the patient's pain evaluation, assessment of the quality, intensity, distribution, alleviating, and aggravating factors is essential.
Patients with thoracic disc herniations may either present with a radicular and/or myelopathic pain depending on if the herniated disc compresses the nerve roots or the spinal cord itself, respectively. With radicular pain, the patients will have pain that follows the dermatomal distribution. Essential landmarks for thoracic disc herniations to help with assessment include T-1 pain that radiates to the medial forearm, T-2 pain that radiates to the axilla, T-4 pain that radiates to the nipple area, T-10 pain that radiates to the umbilicus, and T-12 pain that is just above the inguinal ligaments. The most common initial pain is usually thoracic pain occurring in the midline area. The pain may be unilateral or bilateral depending on the location and how significant the herniation is. The pain may be intermittent and aggravated by coughing and straining. There have been reported cases of pain radiation to the groin, flank, and even the lower extremities.
It is always important to assess other conditions that may be causing the radicular pain. For example, patients with diseases like diabetes and shingles may have similar thoracic dermatomal pain, but in these cases, there will be metabolic abnormalities to prove diabetes and skin rash to point to shingles. It is also essential to rule out other mechanical causes that may lead similar pain syndromes, for example, oblique muscle pain, rib fracture, fracture of the facet joints and clavicle. A detailed patient history is needed to elicit the origin of the pain and to correlate pain with the patient lifestyle. For example, while athletes like baseball and golf players are most likely to have thoracic discogenic pain syndrome, they are also more prone to having pain from the oblique muscle, clavicle, or facet joint pain. Other conditions like patients with malignancies like neurofibroma may also present with thoracic pain syndromes. Assessing skin for cafe au lait spots and other neurofibromas that is associated with this condition is vital for diagnosis.
On the other hand, a patient with myelopathic pain may present with pain corresponding the spinal cord region compressed and lower. The patient may present with lower extremity numbness and weakness, pain, gait abnormalities, hyperreflexia and in rare cases paraplegia. Intracranial and postural hypotension and headache are exceptional, and emergency presentation with thoracic pain may be secondary to calcified disc tearing the dura leading to cerebral spinal fluid (CSF) leak.
Physical examination should include assessment of sensation with pinprick and touch in the upper extremity, thorax, and abdomen in the dermatomal regions mentioned above to check for radiculopathy and also in the lower extremity to check for myelopathy. Also, for the lower extremity, proprioception and reflexes and toned should be evaluated.
In addition to a detailed neurological examination, an MRI of the thoracic spine is very sensitive and specific for diagnosing thoracic disc herniation. In some situations, thoracic discography can be performed to confirm the pain being of discogenic origin being that most thoracic discogenic syndrome can be asymptomatic.
The initial treatment of thoracic discogenic syndrome is usually conservative (nonoperational) since some disc herniations have been reported to stabilize/regress with time, especially in younger patients. Conservative management includes rest, anti-inflammatory drugs, and physical therapy. Drugs like Pregabalin have been reported to be useful for the numbness and radicular pain. Selective spinal root or intercostal nerve blockade and epidural steroids injections can also be used to treat radicular pain.
Surgical intervention is considered as a last resort for the treatment of symptomatic thoracic disc herniations with patients unresponsive to conservative treatment. Surgery will allow for the removal of the ossified disc decompressing the region and relieving pressure on the nerve or spinal cord. Despite advances in thoracic disc herniation surgery, there is still about 20% to 30% complications associated with it. Several factors contribute to these complications. First, symptomatic thoracic disc herniation is rare making it difficult for doctors to gain enough experience to handle it. Secondly, the nature of the thoracic spines makes it difficult to access the herniations. For example, accessing herniations that are located centrally and anteriorly via posterior vertebral column will mean manipulating the thoracic spine that may result in further spinal cord injury and neurological deficits. Accessing centrally located herniations through the anterior transthoracic approach provides an optimal corridor but also involved with high complications and mortalities. Thirdly, herniations that are calcified and adherent the dura risk dura tear during surgery leading to CSF leak and intracranial and orthostatic hypotension and headache.
Thoracic discogenic pain syndrome (TDPS) is rare making it challenging for the healthcare team to diagnose and treat the condition. The rarity of TDPS is attributed to the particular orientation, structure, and function of the thoracic spine in the vertebral column. Despite this rarity, nurse practitioners, physician assistants, and physicians should be familiar with its diagnosis and treatment and work as an interprofessional team to provide treatment. [Level V]
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