Baastrup’s disease
: A rare case report
A 50 years old female farmer presented to us with insidious
onset, gradually progressive low backache of one year’s duration. The
low backache was activity related. There was history suggestive of neurogenic
claudication with the claudication distance being restricted to less than
100 meters. Non-operative treatment taken during this period had not
been effective.
On examination, palpable steps were present
at L3-4 and L4-5 levels. The steps reduced on flexion and increased
on extension. Local spinal tenderness and paraspinal muscle spasm was
present. Extension of the spine was significantly restricted and painful.
No significant tension or localizing signs were present. No neurological
deficit was noted.
X-rays (fig. A&B) of the lumbosacral spine
in the anteroposterior and lateral views showed the presence of grade I anterolisthesis
of L3 over L4 and grade II anterolisthesis of L4 over L5. There was
loss of L4-5 disc space with sclerosis of the adjacent endplates. Significant
facetal hypertrophy was noted at both the levels. MRI (T1 & T2
images) showed the presence of neoarthrosis between the spinous processes
of L3 & L4 with associated interspinous bursitis (fig:C, yellow arrow).
There was also a cyst in the midline in the posterior epidural space at the
same level as the interspinous cyst, with resultant canal compromise (fig:
C, red arrow). There were minimal disc bulges at L3-L4 and L4-5 levels.
The presence of the interspinous cyst was suggestive of Baastrup’s disease.
Since the beginning of this century, Baastrup’s
disease has been a source of controversy as regards its painful nature and
its appropriate treatment. Bywaters and Evans noted pseudojoints, chondroid
metaplasia, enchondral ossification and gross osteoarthritic bone erosion
with eburnation in their autopsy study on these patients. Clinically, these
may produce pain on extension especially if there is lordosis as with obesity,
hip limitation and in champion swimmers. Early reports indicated relief in
pain on injection of local anaesthetic agents. Bywaters suggested that
since there is gross osteoarthritic bone erosion in the approximating spinous
processes and since bone is supplied with sensory nerve endings; this must
be a common cause of localized backache, episodic in nature. Beckers
incriminated the accompanying hyperlordosis as the cause of pain. Similar
views were expressed by Resnick. Haig et al reported that diffuse fatty
replacement of the paraspinal muscles, perhaps due to a compartment syndrome
or other vascular event, might have a role in the pathogenesis of Baastrup’s
disease. Macnab felt that “kissing spines” cannot occur in the absence
of an unstable disc segment and in the balance of probabilities; it is the
associated disc degeneration rather than the bony opposition of the spinous
processes that is the cause of the patient’s symptoms. Goto et al reported
cervical myelopathy due to osteophytic lipping and pseudarthrosis between
the posterior tubercle of C1 and the spinous process of C2. Hazlett
reported the association of spondylolisthesis and Baastrup’s disease.
D
E
F
Surgical treatment was undertaken for our patient. Through the posterior
midline approach, careful dissection was done to identify and dissect out
the interspinous cyst. Attempt at excision of the intact cyst was made.
This revealed the presence of a communicating extension between this cyst
and the second cyst in the posterior epidural space, through the midline
cleft in the ligamentum flavum. The entire cyst was excised. The kissing
spinous processes were then excised. Thorough decompression of the spine
was done. Stabilization of both the segments (L3-4 & L4-5) was done with
posterior Moss Miami fixation, along with intertransverse fusion (fig. E
& F).
Subsequent to the surgery, the patient noted
significant subjective improvement.
To the best of our knowledge, this is the first
case report of Baastrup’s disease causing a cyst formation of an hourglass
configuration leading to epidural extension and compression of the neural
elements. It is our contention that there could be a dynamic element
of compression involved in such cases. The epidural part of the cyst
could be increasing in size on extension with a corresponding decrease in
size in the interspinous part; the phenomenon being reversed on flexion.
We however, have not been able to objectively demonstrate this in the present
case report. We feel that a dynamic MRI would be the best way to demonstrate
this and it should be an essential investigation in future studies of a similar
kind.
