Hypothyroidism and Neuropathies

Does hypothyroidism affect the nervous system? You bet! The peripheral nerve is the most common target in the neurologic system. How does a low thyroid hormone affect the peripheral nerve (you might ask)? I'm glad you asked...

Etiology:

1) accumulation of mucinous deposits resulting in nerve entrapment
2) demyelination secondary to Schwann cell defect
3) vascular nerve damage secondary to hypothyroid induced dysfunction of BBB
4) disruption of axonal transport

Signalment:Typically older dogs, however congenital disease does (rarely) happen. NOTE: dogs are not always overweight, heat-seeking or have flaky-hair coats with peripheral neuropathy signs. 

Clinical signs:A polyneuropathy (multiple nerves affected) is most common. This results in paresis without ataxia and reduced to absent peripheral spinal reflexes. Signs may be mild, to start. 
Cranial nerve deficits such as facial nerve paralysis (VII), vestibular dysfunction (VIII), or laryngeal paralysis (X) are common signs of hypothyroidism. Of course, other things can cause damage to these nerves but don't forget to include hypothyroiism on your differential diagnoses list for patients with a peripheral neuropathy. Hypothyroidism may also cause a myopathy and/or megaesophagus.

Diagnostic tests:T4 is a good first step. If abnormal, a full panel is recommended. 

Treatment options:You guessed it...supplementation!

Prognosis:The neuropathy is likely to improve a little or a lot, after several months with therapy if the axonal degeneration is not too severe. I commonly caution owners to be prepeared for perminent deficits and rejoice when that doesn't happen!
Cranial nerve deficits may persist even with appropriate treatment.

Frequency:
Common in older dogs. Remember they don't need to be over0-weight, heat seaking or even sluggish to get a hypothyroid induced peripheral neuropathy. Cats can be hypothyroid too!

May the luck of the Irish be with you this week! Thanks for reading and have a great week! 

Idiopathic Facial Nerve Paralysis

Idiopathic Facial Nerve Paralysis

I thought we'd continue our theme from last week about peripheral neuropathies and talk about a neuropathy that we all (I think) see fairly regularly: Idiopathic facial nerve paralysis.

What is it?
Idiopathic facial nerve paralysis (IFNP) happens for, ahem, unknown reasons. There is some type of synaptic block that, as of now, has an unknown cause. The facial nerve is a motor nerve that starts in the medulla (brainstem), courses through the skull and bulla on it's way to the face. Other causes of facial nerve paralysis such as hypothyroidism, neoplasia, otitis media, polyps, and rarely neuritis. Remember: you must localize the lesion to the peripheral CN 7 to include IFNP on your list of differential diagnoses!

What does it look like?
The facial nerve innervates the muscles of facial expression in dogs and cats as well as providing innervation to the lacrimal eye glands. Clinical signs are typically unilateral and, result in an inability to move the eyelids (inability to blink), inability to move the lips (dogs may accidentally chew on their lips), lack of ear movement (especially noticeable in cats), and a dry, red eye with possible ocular ulceration.

Clinical Course
Signs are typically acute in nature with rapid progression to full clinical manifestation. Spontaneous resolution occurs in 3-6 weeks. Yay!

Management
Supportive care, such as eye lubricant, and ensuring lip injury is minimized by limiting chewing toys/bones, is the mainstay treatment. Antibiotics, steroids, NSAIDs and other medications do not improve the recovery time!

It's short and sweet this week. Please let me know if you have a specific topic of interest! Have a great week, and keep those consults coming.

Consults are available Monday-Saturday at various times. Check out www.barnesveterinaryservices.com (press the schedule button in the upper right corner) to schedule. Note: Only veterinarians or veterinary staff may schedule a consult.

Hypothyroidism and Neuropathies

Etiology: The peripheral nerve is the most common target in the neurologic system for hypothyroidism. What causes a peripheral neuropathy due to hypothyroidism? I'm glad you asked....

1) accumulation of mucinous deposits resulting in nerve entrapment
2) demyelination secondary to Schwann cell defect
3) vascular nerve damage secondary to hypothyroid induced dysfunction of BBB
4) disruption of axonal transport

Signalment:

• Typically older dogs, however congenital disease does (rarely) happen. NOTE: dogs are not always overweight, heat-seeking or have flaky-hair coats with peripheral neuropathy signs.
  
  

Clinical signs:

• A polyneuropathy is most common. This results in paresis without ataxia and reduced to absent peripheral spinal reflexes. Signs may be initially mild.

• Cranial nerve deficits such as facial nerve paralysis (VII), vestibular dysfunction (VIII), or laryngeal paralysis (X).

• Hypothyroidism may also cause a myopathy and/or megaesophagus.

Diagnostic tests:

• T4 is a good first step. If abnormal, a full panel is recommended.

Treatment options:

• You guessed it...supplementation!

Prognosis:

• The neuropathy is likely to improve a little or a lot, after several months with therapy if the axonal degeneration is not too severe.

• Cranial nerve deficits may persist even with appropriate treatment.

Frequency:

• Common in older dogs! (And recently seen in one cat with vestibular signs. This job always keeps me on my toes, that's for sure!)

This is Neurology Month for the WVMA. If you haven't seen already, there are 4 virtual talks available to WVMA members, and non-members, for CE credit. I do not receive any payment for promoting this but, I am one of the speakers!

Have a great week, and keep those consults coming. Consults are available Monday-Saturday at variable times so please reach out if I can help you with a case.