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Journal of the American Veterinary Medical Association
Volume 261 | Issue 6 (June 2023)

Acute onset of circling and dull mentation in a 1-year-old male neutered domestic shorthair cat.

J Am Vet Med Assoc. June 2023;261(6):1 - 4.
Shelby Scanlin, Jennifer R Michaels

Companion Notes

Case report of Cuterebra larval migration to the CNS in a cat


Introduction on aberrant Cuterebra larval migration

- Cuterebra larval infestation sporadically reported in the veterinary literature

- most small mammal cases of cuterebriasis involve infestations of the skin and sc

- during the summer (June through September)

- when Cuterebra larvae migrate through host tissue

- aberrant larval migration has been reported in the following:

- pharynx

- eye

- thorax

- cribriform plate

- aberrant CNS Cuterebra larval migration

- often result’s in acute, severe, and rapidly progressive neurological signs

- typically affected cats are young to middle age and have access to the outdoors

- clinical signs depend on the path of brain migration

- resulting in a variety of clinical signs such as the following:

- status epilepticus

- blindness

- head pressing

- anorexia

- circling

- abnormal mentation

- postural reaction deficits

- abnormal gait

- cranial nerve deficits

- many affected cats also have a recent history of upper respiratory tract disease

- probably from larval migration from nasal passage through the cribriform plate

- before moving through brain parenchyma

- rare prevalence

- 6 reported cases in dogs

- only 1 of the 6 survived the acute disease phase

- > 20 cases in cats

- prognosis is guarded to poor in most cases

- presumptive diagnosis typically involves the following:

- blood work commonly reveals the following:

- peripheral leukocytosis with eosinophilia

- consistent with parasitic or allergic disease

- hyperglobulinemia

- consistent with systemic inflammation

- brain MRI

- brain imaging often reveals a migrating Cuterebra larval track

- and associated inflammation, edema, and hemorrhage

- CSF analysis: eosinophilic pleocytosis

- treatment suggested in most case reports of feline cerebral cuterebriasis

- ivermectin at various dosages

- 0.2 mg/kg sc once

- 0.3 mg/kg sc q48h for 3 treatments

- 0.3 mg/kg PO q14d for 2 treatments

- 0.4 mg/kg sc q24h for 3 treatments

- simultaneous use of 1 or more of the following also recommended

(to prevent inflammatory or hypersensitivity reactions and infection)

- anti-inflammatory corticosteroids

- antihistamines

- antibiotics


Case report of a 1-year-old, neutered, sex:M indoor-outdoor DSHcat

- history, physical exam, tests and treatment at referring clinician (rDVM)

- history of current vaccination

- presentation 1 week prior for circling and dull mentation

- treatment

- clindamycin, 12.5 mg/kg PO q12h for possible toxoplasmosis

- cat improved initially but declined 2 days before presentation

- at referral for acute development of circling and dull mentation

- neurological examination

- ambulatory with left-sided hemiparesis

- proprioceptive deficits, left side

- blindness, left eye

- absent left menace response

- intact direct and consensual pupillary light reflexes oculus uterque (OU)

- compulsive circling, to the right

- altered mentation (dull)

- physical examination

- dehydration, 5%

- pallor with pale mucous membranes

- bradycardia

- hypotension, moderate

- blood pressure monitoring initiated

- neurolocalization

- depressed mentation can be due to the following:

- forebrain or brainstem lesion

- systemic disease

- compulsive circling to the right could be due to the following:

- forebrain lesion

- vestibular dysfunction

- lack of other vestibular signs made this unlikely

- blindness oculus sinister and absent menace response on the left

- with the following:

- normal pupillary light reflexes

- normal palpebral reflexes OU

- dysfunction in right forebrain or left cerebellum most likely

- left-sided proprioceptive deficits and hemiparesis can occur with the following:

- right forebrain lesion considered most likely

- considering the other deficits

- left brainstem lesion

- left cervical localization

- likely location of the lesion: right forebrain

- differential diagnoses for an acute, progressive right forebrain lesion

(in a young indoor-outdoor cat)

- infectious disease

- FIP, bacterial, toxoplasmosis, or fungal meningoencephalitis

- immune-mediated meningoencephalitis

- parasitic disease (Cuterebra larval migration)

- neoplasia (lymphoma)

- congenital abnormalities (hydrocephalus, porencephaly)

- toxins such as bromethalin

- neurological signs of this typically have a multifocal localization

- CBC and serum biochemistry: unremarkable

- survey thoracic radiography: unremarkable

- MRI of brain

- L-shaped linear track within the brain parenchyma

- extending from right frontal lobe immediately adjacent to cribriform plate:

- cranially to the right caudate nucleus caudally

 - then turning left and continuing through the thalamus

- into left temporal lobe

- T2-weighted and FLAIR hyperintense and T1-weighted hypointense

- moderately ring contrast enhancing with central hypointense region

- focal region of contrast enhancement, within right caudal nasal cavity

- CSF analysis (cerebellomedullary cistern)

- elevated protein at 28 mg/dL with reference at < 25

- high normal nucleated cell count

- 11% eosinophils, 2% medium mononuclear cells, 87% small lymphocytes

- clinical diagnosis: verminous encephalopathy based on the following:

(caused by aberrant Cuterebra larval migration)

- mild inflammation and eosinophils identified on CSF cytology

- MRI findings

- treatment: IV fluids and maropitant

- treatment following diagnosis of CNS Cuterebra larval migration

- ivermectin, 0.4 mg/kg sc q24h for 3 days

- treatment prior to each dose of ivermectin

(to mitigate inflammatory reactions associated with parasite death)

- dexamethasone sodium phosphate, 0.11 mg/kg IV q24h

- diphenhydramine, 4 mg/kg IM q24h

- ampicillin/sulbactam, 50 mg/kg IV q6h

- enrofloxacin initiated but then stopped due to lack of clear indication

- day 5, cat stable and IV medications were discontinued

- cat transitioned to PO medications

- day 6 cat discharged with PO medications

- recheck 1 month after discharge

- neurological examination

- absent left-sided menace

- intermittent inappropriate left foot placement when sitting

- persistent but improved left-sided postural reaction delays

- outcome by phone 24 months after diagnosis: cat doing well at home


“In summary, CNS cuterebriasis represents a neurologic disease more common in cats than dogs, resulting in presentation during summer months with acute onset and often asymmetric, focal or multifocal, intracranial signs preceded by upper respiratory disease…”

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