Lesion localization is one of those things that can be lost, if not practiced. This week, we’re going to work out those muscles.
Maria, is a 13 year old FS Lab
History: Presented to me with a 24 hour history of acute onset difficulty walking.
Neurologic examination:
Mentation: BAR
Cranial nerves: right head tilt, rotary nystagmus, remainder normal.
Gait: Moderate vestibular ataxia, falling right. No hypermetria or intention tremors noted.
Postural reactions: absent right thoracic and right pelvic limbs, normal other limbs
Spinal reflexes: Normal all limbs, normal c. trunci and perineal
Palpation: non painful, normal cervical ROM
You know what you've got to do now, right?
What is the Neuroanatomic Lesion Localization?
There are several ways to go through lesion localization.
OPTION 1:
I like to make lists. Start by listing all of the abnormalities and ALL possible locations that could result in an abnormal finding. For example:
1) Right head tilt - peripheral CN 8 (right), medulla (right), cerebellum (right or left)
2) Rotary nystagmus - same as above
3) Vestibular ataxia - same as above
4) Reduced paw replacement right side - right C6-T2, right C-C5, right medulla, right pons, right or left midbrain, left prosencephalon.
Now, we start to clump things. Well, for starters any animal with cerebellar disease is expected to have hypermetria and/or intention tremors and Maria did not. We can cross out cerebellar disease. What else? What is the one spot where all of the signs can be explained? That's right - medulla on the right! Voila, lesion localization.
OPTION 2:
The other way to work through this is to identify the cranial nerve affected on the exam (in this case, cranial nerve 8), identify the brainstem segment associated with this cranial nerve (in this case, medulla) and then ask yourself if you can identify if she has a) paw replacement deficits b) hemiparesis and/or c) mentation changes. . If not, it is peripheral and if so, it is brainstem.
Differential Diagnoses
Brain stem vestibular disease in an elderly dog without an important prior medical history would suggest the following differential diagnoses:
Degenerative: none
Anomalous: none
Metabolic: Hypothyroidism
Neoplastic/nutritional: Neoplasia of the brainstem
Infectious/inflammatory/idiopathic: meningoencephalitis (infectious or inflammatory)
Trauma: no supportive history
Vascular: Cerebrovascular accident (stroke)
Final diagnosis: cerebrovascular accident (stroke).
Please reach out if you have a case that is troubling you, a client that needs reassurance that you're doing all you can, or simply have a question. I hope you have a great week!