Lesion Localization and Case Building Practice
Lesion localization is one of those things that can be lost, if not practiced. Don't lose it! You're welcome! :)
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 eliminate some things. How do to differentiate peripheral vs. brainstem vs cerebellar disease? 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? Animals with brainstem disease should have a) change in mentation and/or b)ipsilateral paw replacement deficits and/or c) hemiparesis. Maria has paw replacement deficits ipsilateral to the head tilt so she most likely has brainstem disease.
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 a,b, or c from above. 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)
Diagnostic plan
CBC, serum biochemistry, T4, blood pressure, urinalysis. (Screen for causes of stroke and hypothyroidism). Brain MRI +/- CSF tap.
Final diagnosis: Cerebrovascular disease! She was lucky. We didn't find any underlying cause of disease therefore this was considered idiopathic vascular disease. She showed gradual improvement with the addition of meclizine over 3-4 days with a residual head tilt after 7 days. The head tilt is expected to be permanent but isn't always the case.
How did you do? The neurologic examination, when done thoroughly, can be your best diagnostic tool for patients with neurologic disease! Keep practicing.
I hope you are well, and taking care of yourself. If you have a dog or cat with neurologic disease please reach out - I'd love to help.
Happy September 1st!