Case report

Presumptive ascending myelomalacia in a five-year-old shih tzu following a thoracolumbar intervertebral disc extrusion

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Abstract

In this case report, an atypical presentation of progressive myelomalacia (PMM) is described in a five-year-old Shih Tzu following a right-sided Hansen type I intervertebral disc extrusion (IVDE) between the first and second lumbar vertebra. The dog initially presented with acute paraplegia without nociception and signs of spinal shock on neurological examination and underwent a right-sided L1-L2 hemilaminectomy following diagnosis. The neurological status deteriorated rapidly, progressing to thoracic limb deficits despite improving pelvic limb reflexes. Magnetic resonance imaging revealed an extensive intramedullary T2-weighted (T2W) hyperintensity from C5 to L2, strongly suggestive of PMM. Cerebrospinal fluid (CSF) analysis showed mixed pleocytosis with presence of foamy macrophages, and an elevated protein concentration, further supporting the diagnosis. Unlike the typical descending-ascending progression, this case exhibited an exclusively ascending pattern, resembling subacute posttraumatic ascending myelopathy (SPAM) described in humans. Although a definitive diagnosis could not be confirmed due to the lack of histopathology, the importance of recognizing atypical PMM presentations is highlighted in this case and the role of MRI and CSF analysis in diagnosis and clinical decisionmaking is underscored.