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Case Report
The "moustache" sign: Localized intervertebral disc fibrosis and panligamentous ossification in ankylosing spondylitis with kyphosis
Sanjay Behari, Arun Tungeria, Awadhesh K. Jaiswal, Vijendra K. Jain
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India
Address for correspondence:
Dr. Sanjay Behari, Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Rae Bareli Road, Lucknow - 226 014, India E-mail: sbehari27@yahoo.com, sbehari@sgpgi.ac.in
DOI: 10.4103/0028-3886.72186
Abstract
Localized intervertebral disc and ligamentous ossification may precipitate neurological deficits at any time during the natural course of ankylosing spondylitis (AS). We report 2 patients with AS with "moustache' sign (localized intervertebral disc fibrosis and panligamentous ossification) and neurological deficits. One patient had syndesmophytosis (with paraparesis secondary to thoracic spinal canal stenosis), and the other had "bamboo spine" above and below the involved level. A laminectomy in the former relieved paraparesis, and posterior element excision in both the patients relieved focal tenderness and pain; and both of them could lie supine following surgery.
Key words: Ankylosing spondylitis, kyphosis, laminectomy, spine, thoracic canal stenosis
Introduction
Ankylosing spondylitis (AS) is a chronic inflammatory disease of the spine and sacroiliac joints presenting with pain, stiffness and progressive kyphotic deformity. The radiological manifestations of spinal AS are diverse, occur at multiple levels and represent different stages [1] Localized vertebral or discovertebral lesions can develop in about 1.5% to 28% of patients.[2-4] We describe 2 patients with AS with kyphosis, focal disc space fibrosis and ligamentous ossification confined to a single intervertebral level. On sagittal magnetic resonance imaging (MRI), the discovertebral fibrosis/ossification and ligamentous ossification resembled a "moustache." The clinical implications and biomechanical features of this entity are discussed.
Case Reports Case 1
A 52-year-old lady presented with thoracic spine stiffness and kyphosis of 2 years' duration and was positive for human leukocyte antigen (HLA) B27 antigen. Five months before the present admission, she developed focal tenderness at mid-thoracic level due
to which she was unable to lie supine; and 2 months later, she developed paraparesis (grade 3/5) with a neurological level at T10 following a minor fall. The MRI of the spine showed a mild thoracic kyphosis. At the T9-10 intervertebral disc level, corresponding to the apex of kyphosis, intervertebral disc desiccation with signal intensity loss and panligamentous (involving the anterior longitudinal ligament (ALL); apophyseal--facet-joint capsule; interlaminar and interspinous ligament) ossification illustrating the "moustache" sign were the radiological findings [Figure 1a and 1b]. The posterior element ossification extended up to the subcutaneous tissue. At the levels above and below this index level, there was posterior syndesmophytosis; and at L1-L2 level, there was inflammation of the ALL with low signal intensity on T1- and high signal intensity on T2-weighted images (Romanus lesion). The axial computed tomography (CT) of the spine showed vertebral and subchondral sclerosis with right costovertebral arthropathy and left facet joint ankylosis [Figure 1c and 1d]. Following T9-10 laminectomy and excision of the ossified posterior elements and ligamentum flavum, the paraparesis improved to grade 4/5. At 6 month's follow-up, she was walking independently with spasticity in the lower limbs, and there was no focal thoracic tenderness.
Case 2
A 58-year-old man presented with a 5-year history of cervicothoracic stiffness and kyphotic deformity without any neurological deficit. Four months before the present admission, he had restricted flexion-extension thoracic spinal movements and was unable to lie supine due to focal tenderness at mid-thoracic level. The HLA B27 antigen was positive. His plain radiographs revealed a "bamboo" thoracolumbar spine, with multi-segmental intervertebral disc and ligament ossification. There was preserved motion segment at T11-12 level with osteophytosis and end plate sclerosis at adjacent vertebral segments [Figure 2a-d].
The sagittal MRI revealed the "moustache" sign with hypointense signals in the intervertebral discs and ossification of the posterior vertebral ligaments at T11-12 level. The involved T11-12 level corresponded to the apex of the angle of kyphosis. The posterior interspinous and interlaminar ligaments were ossified. The ossification extended upto the subcutaneous tissue. There was significant end plate sclerosis with osteophytosis at the index level [Figures 3a-d and 4a-d]. Excision of the spinous process and calcified posterior elements brought about an instant relief in the focal tenderness at T11-12 level, and he could lie supine.
Figure 1 : Patient 1 : MRI (a and b) showing kyphosis; D9-10 disc dessication, panligamentous ossification [anterior longitudinal ligament (ALL) (thick straight arrow), facet-joint capsule, interlaminar and interspinous ligament ossification (asterisk)] illustrating "moustache" sign; L1-2 Romanus lesion (curved arrow), posterior syndesmophytosis (oblique thin arrow). Axial CT showing (c) vertebral sclerosis; right costovertebral joint subchondral sclerosis (oblique black arrow); and (d) left facet joint ankylosis (oblique white arrow)
Discussion
The "moustache" sign in AS represents intervertebral disc dessication/ fibrosis and panligamentous ossification at
Figure 2: Patient 2: Plain radiographs of thoracic spine (a) lateral; (b) AP view; and lumbosacral spine (c) lateral; (d) AP view showing the "bamboo spine," except at Tll-12 level (straight arrow)
Figure 3: Coronal (a) and sagittal (b) reconstructed thoracic spine CT showing kyphosis, bamboo spine, multiple thoracic disc space narrowing with ossification; and T11-12 preserved motion segment (straight arrow), end plate sclerosis with fusion of posterior elements (curved arrow). The axial image showing extensive end plate sclerosis (c)
Figure 4: Sagittal MRI (a and b) showing bamboo spine with multilevel disc ossification above and below the level of "moustache" sign at T11-12 level. Ossified posterior elements at that level reach up to subcutaneous tissue. Axial image (c and d) showing vertebral sclerosis (straight arrow) without canal compromise (curved arrow)
a focal intervertebral level. Although the appearance of the involved intervertebral disc level was similar in both the patients, it represented two ends of the clinicoradiological spectrum of AS with kyphosis. In the first patient, an early manifestation of the disease was evident at multiple thoracic intervertebral levels in the form of syndesmophytosis and Romanus sign.[15] Disc ossification was not seen at any level. The loss of thoracic sagittal balance was mild. In the second patient, the plain radiographs showed a "bamboo spine." There was decreased disc space with disc ossification at multiple levels. There was also significant thoracic kyphosis. Thus, in the first patient, the "moustache" sign represented the first intervertebral disc space where focal intervertebral disc dessication and multi-ligament ossification had manifested; and in the second patient, it represented nearly the last disc space to undergo ossification.
Despite the differences in the temporal sequence of the occurrence of the "moustache" sign in the natural evolution of the disease in the 2 patients, its clinical manifestations, biomechanical features and implications were similar. Both the patients presented with progressive stiffness and kyphosis of the thoracic spine and focal tenderness at the point of maximum kyphosis, due to which they were unable to lie supine,[6] which was due to extension of posterior element ossification to subcutaneous tissue.[2] Surgical decompression of the posterior elements in both the patients did not influence kyphosis but brought about significant relief in pain, and both could lie in supine position.
The index level in both the patients represented the thoracic vertebral segment where maximum spinal movements occur. In the first patient, early syndesmophytosis caused progressive loss of motion in the segments above and below the index segment; in the second patient, the established "bamboo spine" above and below the index level led to the same consequence.[1,2] Particularly in our second patient, who had an established bamboo spine, a localized stress fracture subsequent to the index level fusion may have precipitated the progression in kyphosis. [7,8] The preserved and exaggerated movements at focal intervertebral level compensated for lack of movements above and below that level. The patients, therefore, continued daily activities until movements at this intervertebral space were also restrained by the spreading ossification. The ligaments of the lower thoracic spine, the junctional zone between rigid upper thoracic spine and flexible lumbar spine, bear a disproportionate strain. Lack of movements above and below this level (due to progressive ligamentous and disc space desiccation, calcification or ossification) increase the "wear and tear" of ligaments at this level, leading to the irreversible cycle of ligament injury,
healing by fibrosis and its subsequent calcification and ossification. Ossification of the interlaminar and interspinous ligaments and the extension of ossification of the posterior vertebral elements to the subcutaneous tissue validate this biomechanical model of injury. The index level represented the apex of the angle of thoracic kyphosis. The posterior ligaments were in a position of constant stretch and therefore more prone to injury when compared to anterior ligaments that remained in a relatively relaxed state. Our patients were able to walk upright following surgery, and the kyphotic deformity was stable; hence surgical correction and stabilization for the kyphotic deformity was not warranted.
What are the implications of the "moustache" sign? In the first patient, the early canal compromise was due to focal intervertebral ligamentous ossification, requiring a laminectomy to relieve spastic paraparesis. In the second patient, despite the significant clinical progression of AS, the spinal canal diameter remained intact. The "moustache" sign, therefore, represents a disproportionate stress on a focal intervertebral segment, which may precipitate sudden neurological deterioration during the natural course of AS.[9] A mild focal tenderness of mid and lower thoracic levels and inability to lie supine are symptoms to be accorded utmost attention. When "moustache" sign is present, MRI of the entire spine facilitates detection of other radiological manifestations of AS, as well as focal discovertebral and ligamentous pseudoarthrosis or ossification^21 It also enables proper measures to be instituted to delay progression of the disease, including medication; maintenance of spinal stability and flexibility (external orthosis and physiotherapy)[2]; and surgery for intractable pain, neurological deficits and progressive kyphosis (spinal decompression, correction osteotomies and instrumented or noninstrumented fusion).[1°]
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Accepted on 14-07-2010
Source of Support: Nil, Conflict of Interest: None declared.
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