17 Gwendolyn J. Levine Imaging modalities are the cornerstone of intervertebral disc herniation (IVDH) diagnosis, and advanced imaging techniques, such as magnetic resonance imaging (MRI), have supplanted the necessity of ancillary diagnostics such as cerebrospinal fluid (CSF) and electrophysiology in the opinion of some practitioners. CSF analysis remains an important tool to diagnose diseases mimicking IVDH, especially in cases where imaging findings are equivocal. CSF analysis is also gaining recent attention in veterinary medicine as a source of prognostic information in the evaluation of patients with IVDH. Electromyography (EMG) and somatosensory evoked potentials (SSEPs) have been used in the research setting to quantify functional recovery following spinal cord injury (SCI); their role in the clinical management of IVDH has been more limited. CSF analysis has the most utility in alerting the clinician to the presence of an inflammatory disease (e.g., granulomatous meningoencephalomyelitis) in cases where imaging results are equivocal or nondiagnostic. Dogs afflicted with myelitis or meningoencephalomyelitis may have their condition exacerbated by the injection of myelographic contrast into the thecal space; therefore, the nucleated cell count of the fluid as well as the microprotein concentration should be determined prior to contrast administration. Most investigators view MRI as superior to myelography or computed tomography for detecting IVDH and differentiating it from diseases that may have similar clinical signs. Between 26 and 82% of CSF samples acquired from dogs with IVDH have parameters outside of accepted reference ranges (Table 17.1) [1–4]. The most common abnormality observed in patients with IVDH is albuminocytologic dissociation. This occurs when there is an elevation in CSF microprotein concentration without a corresponding pleocytosis (elevated cell count) and may indicate leakage of protein through the blood/spinal cord/CSF barrier. Table 17.1 Cerebrospinal fluid (CSF) characteristics in dogs with intervertebral disc herniation (IVDH) The least common finding in analysis of the CSF from IVDH dogs is that of a pleocytosis (23–61% of assessed samples). Reports vary widely in the literature regarding what type of pleocytosis is the most common. Some authors found that mixed cell pleocytoses are the most common, while others state that neutrophilic pleocytosis is the most often diagnosed [3, 5]. Still other researchers state that lymphocytic pleocytosis occurs with the highest frequency [2]. Even eosinophilic pleocytosis has been reported with IVDH, although thus far it has not been seen with great frequency in any case series [6].
The Role of Nonimaging-Based Diagnostic Studies for Intervertebral Disc Herniation
Introduction
CSF analysis: Typical findings in IVDH
Site
No. of animals
Acquisition location
% Abnormal
Protein range, mg/dl
NC/µl range
Cytology
Ref
C
111
Lumbar
82% (85/104)
protein increased
23% (26/111) NC increased
10–306 (median, 60)
0–54 (median, 2)
Lymphocytic (11/26)
Neutrophilic (8/26)
[6]
C
25
CM
44% (11/25)
Median, 21
0–12 (median, 2)
Mononuclear
[1]
TL
312
Lumbar
66% (152/232) protein increased
61% (190/312) NC increased
3–1920 (median, 57)
0–428 (median, 8)
Lymphocytic (78/190)
Neutrophilic (60/190)
[6]
TL
54
CM
54% (29/54) NC increased
16% (4/25) increased protein
0–228.5 (median, 4.2)
0–104 (median, 6)
Neutrophils most common cell type (60%)
[4]
TL
54
CM
51% (28/54) protein increased
31% (17/54) NC increased
12–110 (median, 28)
0–245 (median, 3)
Neutrophilic (12/17)
Mixed (4/17)
[5]
TL
35
CM
26% (9/35)
10–42 (mean, 19)
0–11 (mean, 2)
N/A
[5]
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