Meningoencephalitis

Written by Dr. Patty Khuly, VMD MBA

Summary

Meningoencephalitis is a term that describes the simultaneous swelling of the tissues that line the central nervous system (the meninges), as in the process known as meningitis, and of the brain itself, as in encephalitis. As such, meningitis is a general term for a variety of devastating neurologic diseases that manifest this way.

Both dogs and cats (though less often) are subject to disorders characterized by meningoencephalitis. These conditions may be categorized as being of either infectious or noninfectious origin:

Causes of infectious meningoencephalitis include bacteria, viruses, fungi, protozoan parasites, rickettsia, and migrating parasites. Causes of noninfectious meningoencephalitis include poisoning and immune-mediated disorders, with the balance classified as idiopathic (which means their cause is effectively unknown).

The following are all examples of disorders that fall under the umbrella of noninfectious meningoencephalitis:

  • Granulomatous meningoencephalitis

  • Pug dog encephalitis

  • Necrotizing leukoencephalitis

  • Steroid-responsive meningoencephalitis

  • Steroid-responsive meningitis/arteritis

  • Eosinophilic meningoencephalomyelitis

  • Pyogranulomatous meningoencephalomyelitis

  • A genetic predisposition may be presumed for some of these noninfectious diseases.

While some of these diseases are fairly rare and somewhat esoteric but granulomatous meningoencephalitis is fairly common and relatively well-understood. This disease is treated in greater depth in a separate article within this library.

Symptoms and Identification

Initially, the most common signs of meningoencephalitis can be vague. Generalized pain or discomfort is often noted but "not acting herself" is a typical owner complaint early on. As the course of the disease progresses, however, one or more of the following signs may be observed:

  • fever

  • neck rigidity

  • muscle spasms

  • blindness

  • progressive weakness

  • loss of balance

  • seizures

  • agitation

  • dementia

  • disorientation

At their most severe, clinical signs may progress to profound depression and even coma.

What's worse, diagnosing the disease can be complicated by its confusing signs and the specialized nature of its diagnosis. Not only are the vagueness of the early clinical signs and the broad range of potential infectious agents a serious impediment, the only effective test for meningoencephalitis requires a specialized test most veterinarians aren't equipped to perform: cerebrospinal fluid analysis (aka, "spinal tap").

This is why many pets are diagnosed with meningoencephalitis on the basis of their clinical signs, the identification of a causative infectious agent, and/or their response to treatment.

Whenever possible, however, board-certified veterinary neurologists or internal medicine specialists are strongly recommended if meningoencephalitis is suspected. A neurologist is well-trained in performing CSF taps. Once a CSF tap is undertaken, CT scans and MRIs may be helpful in confirming this diagnosis and/or in identifying the disease's origins. These tests, too, typical of the specialist's domain.

Affected Breeds

Any breed can be affected by meningoencephalitis. However, breed predispositions for several of the noninfectious meningoencephalitic disorders have been identified. For example:

Treatment

Treatment of noninfectious meningoencephalitis was once relegated to the realm of anti-inflammatory medications like corticosteroids (such as prednisone). Additional immunosuppressive drugs were often employed in concert with these. However, in recent years, the use of radiation therapy has become more popular by way of targeting specific brain lesions that characterize certain manifestations of the disease.

In cases of infectious meningoencephalitis, treating the underlying infection is the ideal approach. This, of course, presupposes that it first be identified.

Sadly, however, this disease is often fatal and treatment may be of little benefit. The exception is for cases where bacterial agents can be identified and eliminated or in the case of steroid-responsive versions.

Veterinary Cost

The cost of meningoencephalitis can be prohibitive unless a presumptive diagnosis and an obviously treatable form of the disease is amenable to rapid treatment. The cost of CSF tap alone can run upwards of $1,000 and the battery of simpler screening tests that precede it can add up quickly.

Prevention

Prevention generally isn't considered feasible for patients predisposed to these diseases. They're rare enough and their genetic underpinnings aren't well enough understood for altered breeding practices to make a difference.

In the case of infectious causes, prevention is indeed possible by adhering to regular parasite prevention regimens and routine vaccination protocols.

References

Adamo F, O'Brien R (2004). "Use of cyclosporine to treat granulomatous meningoencephalitis in three dogs". J Am Vet Med Assoc 225 (8): 1211-6, 1196. doi:10.2460/javma.2004.225.1211. PMID 15521442.

Chrisman, Cheryl; Clemmons, Roger; Mariani, Christopher; Platt, Simon (2003). Neurology for the Small Animal Practitioner (1st ed.). Teton New Media. ISBN 1-893441-82-2.

Ettinger, Stephen J.;Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-

Garosi, Laurent S. (2006). "CNS inflammatory (UK) problems: The neurologist's viewpoint, clinical approach and treatment" (PDF). Proceedings of the 53 degrees Congresso Nazionale Multisala SCIVAC.

Gelatt, Kirk N. (ed.) (1999). Veterinary Ophthalmology (3rd ed.). Lippincott, Williams and Wilkins. ISBN 0-683-30076-8.

Higginbotham, Michael J.; Kent, Marc; Glass, Eric N. (August 2007). "Noninfectious Inflammatory Central Nervous System Diseases in Dogs". Compendium on Continuing Education for the Practicing Veterinarian (Veterinary Learning Systems) 29 (8): 488-497.

Schatzberg S, Haley N, Barr S, de Lahunta A, Sharp N (2005). "Polymerase chain reaction screening for DNA viruses in paraffin-embedded brains from dogs with necrotizing meningoencephalitis, necrotizing leukoencephalitis, and granulomatous meningoencephalitis". J Vet Intern Med 19 (4): 553-9. doi:10.1892/0891-6640(2005)19[553:PCRSFD]2.0.CO;2. PMID 16095173.

Suzuki M, Uchida K, Morozumi M, Yanai T, Nakayama H, Yamaguchi R, Tateyama S (2003). "A comparative pathological study on granulomatous meningoencephalomyelitis and central malignant histiocytosis in dogs". J Vet Med Sci 65 (12): 1319-24. doi:10.1292/jvms.65.1319. PMID 14709820.

Vernau, William (2005). "Cerebrospinal Fluid Analysis in Dogs and Cats" (PDF). Proceedings of the 50 degrees Congresso Nazionale Multisala SCIVAC.

Vite, C.H. (2005). "Inflammatory Diseases of the Central Nervous System". Braund's Clinical Neurology in Small Animals: Localization, Diagnosis and Treatment.