JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 2237869): 6-year-old Morgan horse gelding
HISTORY: This horse had slowly developed posterior ataxia over the last few months, and recently had been unable to defecate. At presentation, the tail and anus were flaccid. The hindquarters, tail, and tailhead were without sensory perception.
HISTOPATHOLOGIC DESCRIPTION: Spinal cord, cauda equina: Diffusely, extradural and fewer intradural spinal nerve roots are surrounded and widely separated by abundant dense bands of fibrous connective tissue (fibrosis). The perineural epithelium is hyperplastic, up to three times normal, and the fibrous perineurium is markedly thickened by collagen and blends with the surrounding epineurium. There is multifocal infiltration of perineuria, nerve fascicles and ganglia by numerous lymphocytes and macrophages, fewer plasma cells, rare hemosiderin‑laden macrophages, and scattered hemorrhage. Ganglion neuronal perikarya are swollen and exhibit central chromatolysis (degeneration). Within the spinal cord and nerve roots there are occasional dilated and empty myelin sheaths and swollen, hypereosinophilic axons (spheroids).
MORPHOLOGIC DIAGNOSIS: Spinal cord, cauda equina: Polyradiculoneuritis and ganglioneuritis, lymphohistiocytic, chronic, diffuse, moderate, with marked epineurial and perineurial proliferation and fibrosis, hemorrhage, and axonal degeneration, Morgan, equine.
ETIOLOGIC DIAGNOSIS: Idiopathic polyradiculoneuritis
CONDITION: Cauda equina syndrome
SYNONYMS: Neuritis of the cauda equina; polyneuritis equi
· Granulomatous, fibrotic and demyelinating disease of unknown etiology affecting peripheral nerves in the horse
· Uncommon, progressive inflammatory condition primarily involving the extradural portions of the nerve roots of the cauda equine
· Occasional involvement of cranial nerves and autonomic nervous system
· No breed, age or sex predilection
· Poor prognosis
o Nature of the reaction suggests immune mediation, which may follow viral infection (e.g. persistent herpesvirus infection)
o May represent an allergic, post-infectious, or post-traumatic neuritis
o Halicephalobus gingivalis reported as a novel cause in one horse
o Persistent adenovirus and herpesvirus-1 have been implicated on inciting an immune-mediated inflammatory reaction
TYPICAL CLINICAL FINDINGS:
· Signs of lower motor neuron lesions primarily referable to the sacrococcygeal nerves—hypotonia, hypalgesia, and hyporeflexia of the tail, anus, and perineal region; urinary bladder paresis with sabulous cystitis and rectal dilatation
· Rear limb weakness and ataxia; muscle atrophy
· Cranial nerve involvement, especially V and VII, but also VIII, IX, X, and XII— muscle twitching and atrophy, facial paralysis, hyperesthesia, and ataxia (vestibulocochlear nerve (VIII) involvement)
· Lumbar cerebrospinal fluid analysis: Elevated protein level, with increased monocytes and neutrophils
· Nonspecific neutrophilic leukocytosis and hyperfibrinogenemia
TYPICAL GROSS FINDINGS:
· Extradural segments of sacral and coccygeal nerves are thickened and can form a fibrotic mass, edematous, and discolored by hemorrhage
· Extension through intervertebral foramina into adjacent muscle
· Intradural nerve segments are discolored, but not usually enlarged
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Acute lesions consist of hemorrhage and inflammation of extradural nerves
· Chronic lesions of nodular, granulomatous inflammation and centrally located epithelioid macrophages and giant cells with extensive fibrosis; granulocytes are NOT a feature of the infiltrate
· Abundant epineural and perineural proliferation of extradural root sheaths and demyelination
· Secondary axonal degeneration
· Inflammation spares the muscles which exhibit secondary changes of neurogenic atrophy
· Sacral or coccygeal trauma
· Equine herpesvirus type 1 myeloencephalitis, vasculitis
· Equine protozoal myeloencephalitis (Sarcocystis neurona): Necrotizing, nonsuppurative encephalomyelitis; occasional hemorrhage; perivascular, primarily mononuclear inflammation of gray and white matter (lymphocytes, plasma cells, macrophages, and occasional eosinophils), schizonts
· Rhodococcus equi myeloencephalitis (secondary to vertebral osteomyelitis)
· Nematode migration (Strongylus vulgaris; Halicephalobus deletrix)
· Rabies (Rhabdoviridae; lyssavirus): Nonsuppurative polioencephalomyelitis with ganglionitis, Negri bodies
· Cauda equina syndrome in dogs: Due to lumbosacral stenosis and/or stenosis of the intervertebral foramina, German shepherd dogs and Border collies predisposed
o Guillain-Barré syndrome in humans (acute inflammatory demyelinating polyradiculoneuropathy): Ascending paralysis; inflammation and demyelination of peripheral nerves and spinal nerve roots; usually preceded by a viral-like illness or history of recent vaccination; immunologically-mediated process
· Experimental allergic neuritis (EAN) in laboratory animals (Lewis rats and rabbits): Animal model for Guillain-Barre syndrome, with similar lesions induced by immunization with myelin or myelin proteins; transient paralysis; autoimmune disorder thought to be due to both T-cell mediated and humoral immune response
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