Mya, 7 year-old, FS, Doberman Rescue
History
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.
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 the 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
The general exam is normal with the exception of a firm bony protrusion from the left frontal bone (over frontal sinus).
What does it mean when the gait is normal and there is marked postural deficit on the right side?
The 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 localized to the right mandibular nerve (possibly brainstem) and the left forebrain.
Marked temporalis muscle asymmetry on MRI: Blue Arrow – normal temporalis muscle on left Red Arrow – atrophied temporalis muscle on right.
Differential Diagnosis (possible causes)
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
Red star – atrophied pterygoid muscle on right Red circle – atrophied masseter muscle on right. Blue star – normal pterygoid muscle on left. Blue circle – normal masseter muscle on the left. Mandibular nerve lesion inferred from masticatory muscle atrophy – ptosis is from pterygoid muscle atrophy (notice how it abuts the right eye).
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:
1)Head trauma and hydrocephalus ex vacuo (fluid where there was brain).
2)Unknown / Idiopathic right mandibular nerve lesion with neurogenic masticatory muscle atrophy.
Red circle – boney mass over depressed left frontal sinus.
Red star – fluid space in left parietal and frontal lobes.
Head trauma leading to bone callus and loss of brain (hydrocephalus ex vacuo).
Take Home 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!
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