Introduction

• See also granulomatous meningoencephalomyelitis (GME) Granulomatous meningoencephalomyelitis , aseptic suppurative meningo-arteritis (= steroid responsive meningitis Steroid-responsive meningitis-arteritis (SRMA) ), breed specific meningitis.
• Inflammation of the meninges. Associated with necrotizing fibrinoid arteritis in the context of aseptic suppurative meningo-arteritis.
• Cause: infectious, eg bacterial, immune-mediated, idiopathic, eg aseptic suppurative meningo-arteritis → specific syndromes (Beagle, Bernese Mountain dog, Boxer, Weimaraner, Nova Scotia Duck Tolling Retriever, German Short-haired Pointer).
• Signs: Hyperesthesia, fever, cervical pain, cervical rigidity.
• Diagnosis: signs, CSF tap.
• Treatment: antimicrobial agent for infectious cause (rare), immune-suppressive treatment for aseptic suppurative meningo-arteritis.
• Prognosis: poor long-term.

Pathogenesis

Etiology

• Aseptic suppurative meningo-arteritis (= steroid responsive meningitis Steroid-responsive meningitis-arteritis (SRMA) : idiopathic.
• Bacteria: usually Staphylococcus spp Staphylococcus spp , Pasteurella spp Pasteurella multocida.
• Viruses: canine distemper virus Canine distemper disease , parvovirus Parvovirus disease associated with CPV-2 , parainfluenza virus, rabies virus Rabies disease , herpes virus Canine herpesvirus , La Grosse Virus.
• Rickettsiae and chlamydiae: Rickettsia rickettsii (Rocky Mountain spotted fever) Rocky Mountain Spotted Fever (RMSF) , Ehrlichia canis (ehrlichiosis) Ehrlichiosis.
• Spirochaetes: Borrelia burgdorferi (Lyme disease Arthritis: borrelial ), Leptospira spp Leptospirosis.
• Protozoa: Toxoplasma spp Toxoplasmosis , Neospora spp Neosporosis.
• Fungi: Nocardia spp Nocardiosis , Actinomyces spp Actinomycosis , Aspergillus fumigatus Aspergillosis: disseminated , Cryptococcus neoformans Cryptococcosis , Blastomyces dermatidis Blastomycosis.
• Algae: Prototheca spp Protothecosis.

Predisposing factors

General

• Bacterial endocarditis Endocarditis: bacterial.

• Trauma, eg bite wound.
• Contaminated surgical instruments.
• Previous infection with canine distemper virus.

• Dog originating from USA or mainland Europe.
• Exposure to ticks, Rocky Mountain spotted fever, ehrlichiosis.

Specific

• Ticks - European tick-borne meningoencephalitis (TBE).

Pathophysiology

• Bacterial invasion of the CNS usually → both meningitis and encephalitis. Such infections occur via hematogenous spread from distant foci within the body: direct extension from sinuses/ears/eyes; as a result of trauma, eg bite wound; and from contaminated instruments, eg spinal needle.
• Note that one important source of bacterial infection of meninges/CNS parenchyma in dogs is bacterial endocarditis.
• Organisms usually disseminate via CSF pathways and → cerebrospinal meningitis, often associated with micro abcess formation in brain/spinal cord.
• Aseptic suppurative meningo-arteritis is a systemic immune disorder.
• Meningitis and vasculitis - partial/complete vessel occlusion as a result of fibrinoid necrosis of vessel walls and periarteritis in meninges often leads to ischemia/thrombi.
• Vasculitis is more common in the leptomeninges of the spinal cord than around the brain.
• Lesion occasionally present in the thyroid, heart and mediastinum.

• Pyrexia is thought to be secondary to bacterial invasion of the blood stream and CSF, accompanied by the release of leukocytic pyrogens and hypothalamic stimulation.
• In humans, inflammation of the subarachnoid space activates protective reflexes, which result in nuchal rigidity and hyperextension of the neck and vertebral column.
• A similar mechanism probably exists in dogs showing signs of cervical rigidity and occasionally seen opisthotonus and thoracic limb hyperextension.
• Seizures may be caused by high fever, hypoglycemia, brain edema or inflammation.
• Vomiting may result from increased intracranial pressure or from direct effects on the vomiting center.
• In some animals, chemical signs may suggest CNS parenchymal involvement.

Timecourse

• Often acute/hours/days.

Diagnosis

Treatment

Outcomes