Mya
2023
MEET MYA
Mya is a seven-year-old rescued Doberman. She and her sister were placed into foster care. Since she was young, there has been a bump on the left side of the top of her head.
General exam is normal with exception of firm bony protrusion from the left frontal bone (over frontal sinus)
PRESENTING COMPLAINT
Right thoracic limb sliding out to the side and occasional stumbling and knuckling on RTL
Droopy right eye
Possible leaning to the left and less energy than her sister
MENTATION
(level of awareness, presence of confusion)
Quiet, but seemingly normal. She kept raising her paw for attention
GAIT - NORMAL
POSTURE
(body position, things noted by just looking at patient)
Occasional / possible left head tilt
Occasionally holds right thoracic more than right pelvic limbs abducted (away from midline)
Bump over her left frontal sinus
Ptosis on right eye
POSTURAL REACTIONS
(ability to correct position of a limb)
Very slow paw flip test on right side (worse on the thoracic limb
CRANIAL NERVES
Ptosis OD
No positional strabismus when head elevated
No inducible vestibular signs
HYPERAESTHESIA – NONE APPRECIATED
WHAT DOES IT MEAN WHEN THE GAIT IS NORMAL AND THERE IS MARKED POSTURAL DEFICIT ON THE RIGHT SIDE?
There is a lesion is within the left forebrain.
DOES THE OCCASIONAL HEAD TILT INDICATE A VESTIBULAR LESION? WHY OR WHY NOT?
The absence of a positional strabismus or any consistent vestibular makes a vestibular lesion very unlikely.
WHAT IS THE LIKELY CAUSE OF PTOSIS IN THIS CASE?
Mandibular nerve lesion involving the pterygoid muscle.
WHAT IS THE LIKELY CAUSE OF THE UNILATERAL MANDIBULAR NERVE LESION (MASTICATORY MUSCLE ATROPHY)?
Never Type 2 M autoantibodies - most often a peripheral nerve sheath tumor.
CAN YOU EASILY MAKE THIS ONE LESION?
No – I localize to the right mandibular nerve (possibly brainstem) and the left forebrain.
DIFFERENTIALS
Left forebrain (postural deficit, normal gait):Neoplasia, inflammation, malformation, unknown, infection, infarct(s)
Right mandibular nerve +/- brainstem (temporalis and pterygoid atrophy): Neoplasia (nerve sheath tumor, meningioma, lymphoma), inflammation, unknown, infection, infarct(s)
PLAN
CBC, Chem, Contrast MRI of the brain +/- CSF
RESULTS
CBC, Chemistry – normal
MRI of the brain:
Boney lesion within left frontal bone and loss of brain from the left forebrain – past trauma most likely.
Masticatory muscle atrophy and no lesion noted within the brainstem or mandibular nerve– cause not determined, inflammation/infection possible, recommend CSF analysis
CSF analysis: normal – infection and inflammation not likely
DIAGNOSIS
Head trauma and hydrocephalus ex vacuo (fluid where there was brain).
Unknown / Idiopathic right mandibular nerve lesion with neurogenic masticatory muscle atrophy
IMPORTANT POINTS
Normal gait with markedly abnormal postural reactions indicates a lesion on the side opposite the postural deficit.
Ptosis can be from pterygoid muscle atrophy.
Elevating the head and looking for positional strabismus is a good way to evaluate for vestibular disease.
Unilateral masticatory is never from immune-mediated masticatory myositis and often from a nerve sheath tumor.
Multifocal localizations are confusing and often from inflammatory disease, but not always!
