I read an interesting article recently about positioning head tilts in cats with hypokalemia myopathy (https://doi.org/10.1177/1098612X231175761) This isn't likely to be something you encounter often in practice, but I hope you will also find it an intesting read nontheless.
Hypokalemic myopathies are common in cats and often result in signs of weakness including cervical ventroflexion and/or tetraparesis. We can see hypokalemia secondary to renal disease, hyperthyroidism, dietary insufficency, chronic vomiting/diarrhea, and other metabolic causes. The subsequent myopathy occurs due to overpolarization of the muscle sarcolemma resting membrane potential making it resistant to depolarisation. Without depolarization, there is no muscle contraction and we see clinical weakness.
When the head is turned, the cerebellum (specifically the nodulus and uvula) receive input from the vestibular nuclei, who in turn receive sensory information from the stretch receptors in the cervical muscles, on the whereabouts of the head and neck. This allows the cerebellum to modify the head position so that the head remains paralell to the ground as it is turned. With positioning head tilts, the head tilts to the opposite direction that the head is turning. When looking straight, no head tilt is observed. When turning right, the head tilts slightly to the left, for example.
This article described 14 cats who had a positioning head tilt obseved on neurologic examintation AND had concurrent hypokalemia. One cat had an MRI and no cerebellar lesions were noted. Does that mean the others didn't? No, of course not. However, when the potassium was normalized the positional head tilt resolved. This would suggest cause and effect but isn't definative. The authors supposed that the muscle firing in the spindle fibers (the very small muscles located in the bigger muscles that convert stretch to neuronal impulse for sensory information) weren't able to depolarize appropriately. This lack of depolarization resulted in an absence of information about the whereabouts of the cervcial muscles (and those attached to the head, specifically) and didn't allow the cerebellum to modify head posture when turning. Pretty cool, huh? Although this is just a therory, I personally think it is pretty slick and clever.
Take home message:
What do you do with a positioning head tilt in a cat? Look for hypokalemia and if identified, address it!
Do you know that I'm in charge of my own schedule? I'm not corporate or owned by anyone! So if you cannot find a suitable time on the scheduler please email me! I will do my best to find an earlier time to accommodate a more urgent case. Some of you lovely, considerate, folks have told me that you hate to bother me to ask. If you're one of those, please know you're not a bother. We're both trying to work on behalf of your patient!
Have a great week. I hope you enjoyed this little TidBit as much as I did. I look forward to working with you soon!
Limber Tail?
Limber tail, or cold tail, is known medically as coccygeal myopathy and is a poorly characterized condition associated with acute onset tail flaccidity and pain. Working dogs are more commonly associated with the disease, especially hunting breed dogs. I recently evaluated a patient with suspected "limber tail" and thought it might be fun for us all to review this unusual disease. The most recent study published was 2016, so I'll reference data from that study in this TidBit Tuesday. Reference at the end.
What is the pathology associated with limber tail?
Limber tail is a self-resolving disease, usually within 10 days of the onset of signs, therefore very little pathology has been described for the problem. One study from Norway in 1999 identified inflammatory cells in the coccygeal muscles along with evidence of myofiber damage and elevated CK in dogs with clinical evidence of limber tail, compared to breed matched control (nonclinical) dogs.
What are common triggers?
In a questionnaire to dog owners in the UK (2016) the following triggers were queried and the responses are as follows:
Swimming (29 yes, 9 no)
Exposure to cold weather ( 19 yes, 19 no)
Exposure to wet weather (11 yes, 26 no, 1 unsure)
Vigorous exercise (18 yes, 18 no, 2 unsure)
Confinement (5 crate, 1 car, 31 no, 1 unsure)
Some triggers appeared to be dual, such as swimming on a cold day. Increasing latitude has been identified as a risk factor, which is assumed to be linked to colder temperatures. They determined that while swimming was not a necessary precursor to the development of limber tail, it appeared to be a risk factor. The odds ratio of a swimming case compared to control was 4.7. Furthermore, cases were more related (had common ancestors) compared to controls and this was more than is expected for random selection. Otherwise, a similar distribution between cases and controls was noted for neuter status, coat color, height, weight, exercise levels, household type, and smoking vs non-smoking in the home.
Do you need to treat it?
The self-resolving nature has made treatment protocols difficult to evaluate. Pain management in the early phases, as needed, is appropriate. This could include anti-inflammatory medications such as NSAIDs, but probably doesn't need to rise to the level of steroids in most dogs. Pain modulation with gabapentin, narcotics if severe pain is noted, or muscle relaxants could be utilized. If clinical signs have not resolved by day 10, additional diagnostic testing such as MRI of the lumbo-coccygeal region, electrodiagnostic testing or both may be indicated.
I hope you enjoyed Labor Day holiday and weekend and have a great week! I am in town this week but leaving for a few days over next weekend to speak at IVECCs in beautiful Denver Colorado. I will have limited email and telephone access Monday-Tuesday September 11-12th due to travel and speaking hours. Please pardon my delay in response if you reach out on those days. Thanks for reading!
Reference: https://bvajournals.onlinelibrary.wiley.com/doi/epdf/10.1136/vr.103729
Cushing's Induced Muscle Weakness
Hyperadrenocorticism (HAC) or Cushing’s disease is a common cause of muscle weakness. Biopsies have shown that type II muscle fiber atrophy is common and clinical signs have included weakness in all four limbs, along with muscle atrophy. A less common form of HAC myopathy is a severe muscle stiffness (SMS) that results in a stiff or stilted gait. A recent study evaluated the signalment, presentation and treatment options along with long-term outcome in a collection of 37 dogs diagnosed with HAC.
What is HAC induced Severe Muscle Stiffness?
As the name suggests, the clinical manifestation of the unusual form of HAC myopathy includes stiffness of pelvic or all four limbs. The etiology is unknown but electrodiagnostic evaluation suggests a myotonia. Myotonia is defined as a sustained contraction after percussion (hammer reflexes) or voluntary contraction. The muscle will occasionally ripple visibly, but usually a prolonged limb stiffness can be seen. Dogs with HAC induced SMS have a ridged, stiff-legged gait when moving and don’t demonstrate appropriate joint flexion. According to Golinelli et al (DOI: 10.11.11/jvim.16620) over 60% of dogs had only the pelvic limbs affected at the time of diagnosis, the remainder had all four limbs affected. An elevated CK was noted in 75% of the dogs, suggesting muscle membrane breakdown or injury.
It was interesting to note that the diagnosis of SMS was more common in small breed dogs, weighing less than 15 kg. The time of SMS diagnosis varied in reference to the HAC diagnosis. Almost 62% were diagnosed 1 month to 3 years after being diagnosed with HAC, 8% were diagnosed with HAC and SMS at around the same time and 30% were diagnosed with SMS 1 month to 1 year BEFORE being diagnosed with HAC. There are many reasons for these findings including owner or veterinarian awareness of SMS, lack of ability to test for or diagnose HAC, or perhaps a pathologic change/trigger required to convert from HAC with weakness to SMS.
How is it treated?
In short, poorly. In the report cited above, no single treatment resulted in effective resolution of the clinical SMS. Therapeutic intervention included benzodiazepine drugs (19% of cases), physiotherapy (16% of cases), acupuncture (5% of cases), and one or two dogs received mexiletine, NSAIDs, dantrolene, botulin toxin, L-carnitine, methocarbamol, gabapentin, and cannabinoids. Mild improvement was reported with some treatments. Survival of dogs with HAC induced SMS was unchanged compared to survival of dogs with HAC only.
Key points:
Be aware that SMS can occur with HAC
The reason a dog will have SMS instead of muscle weakness is unknown
No specific treatment resolved signs in all dogs, however there are several reasonable treatment choices listed above to try.
Thanks for reading! Enjoy the first day of Spring!
Myoclonus - what does it mean?
Myoclonus is defined as a sudden onset jerking motion. How is this different from a tremor? Tremors tend to have a creshendo, decreshendo appearance where as myoclonus has been described as "square form" impulse with sudden, rapid onset, sustained contraction, and sudden stop. Okay, fine, it's not a tremor. How do I diagnose myoclonus?
There are four common types:
1) Physiologic - the classic example is hiccups.
2) Epileptic- occur with or around epileptic seizures
3) Idiopathic - unknown origin or cause (rare in veterinary medicine...or we're just missing it.)
4) Symptomatic - due to an underlying pathology. For example, distemper virus.
Neuroanatomic lesion localization:
1) Cortical - usually associated with myoclonic seizures.
2) Subcortical (brainstem) - "falling asleep" myotonia. In this case, people or animals will suddenly "jerk" just as they fall asleep. Classically, this has been thought to occur because the cortical functions "turn off" before the brainstem functions but this may not be the complete story.
3) Peripheral - an example is hemifacial spasms, or ocular spasms (have you ever had your eyelid twitch annoyingly and you cannot stop it?)
Veterinary neurologists are often consulted for symptomatic and epileptic myoclonus. Although there is a population with idiopathic myoclonus, it is rare. Symptomatic myoclonus occurs at rest, asleep, or during motion. Symptomatic myoclonus does not stop with sleep! The animal may appear aware or unaware of the twitch. If the contraction is happening in a body part used for walking or eating it may be life limiting. If not, animals may live with a myoclonus with minimal disruption. Epileptic myoclonus occurs around a time of seizure activity and is therefore often managed with anticonvulsant management.
Distemper virus is a common cause of canine myoclonus and CNS infections (various causes) have been cited as causes of feline myoclonus. There is no treatment available for distemper virus therefore, patients are monitored for progressive neurologic signs (mentation changes, gait changes, seizures, other) and euthanized if signs are progressive. If the signs are not progressive, usually myoclonus is not a reason for euthanasia.
That's all I have for you today! I hope you enjoyed this TidBit about myoclonus and feel better prepared when you see it in your exam room. :)
Thank you for reading! May you have a wonderful, twitch-free holiday week!
Masticatory Muscle Myositis: That's a mouthful!
We are seeing more cases of masticatory muscle myositis lately so I thought we'd look into this interesting diagnosis together. Let's start by defining it.
Masticatory Muscle Myositis (MMM) is an inflammatory, autoimmune myopathy affecting the muscles of mastication (temporalis, masseter, pterygoid and rostral digastricus). All of these muscles are innervated by CN 5, specifically the mandibular branch.
Why only these muscles?
The muscles listed above have a specific myofiber type (type 2M), which is only present in these muscles and some fetal muscles. All other muscles in the body are 1A and 2A fiber types! Therefore, these muscles present a unique antigen for the immune system to target.
What does the clinical picture look like?
There is an acute phase, and a chronic phase. The acute phase occurs first and often includes signs such as jaw pain, swollen muscles, and difficulty chewing. (Note NOT drop jaw or difficulty closing the jaw....that is a different disease.)
If left untreated, patients will then progress into the chronic phase, which includes signs such as muscle atrophy and an inability to open the jaw. Muscle fibers are replaced with scar tissue during the chronic phase making the dog unable to open their mouth more than a few centimeters over time.
Must we take a chunk of muscle to make this diagnosis?
No, you don't! Although you will obtain a diagnosis in both the acute and chronic phase, there is an easier, and less invasive, way. The serum 2M antibody test is both highly sensitive (85-90%) and highly specific (100%) and is the preferred diagnostic test for MMM. Send it to the Comparative Neuromuscular Lab in La Jolla CA (https://vetneuromuscular.ucsd.edu/) if you live in the states. I think there are other choices worldwide but I'm not as aware of those.
Steroids are the best, and most effective treatment.
Immunosuppressive steroids are the most effective treatment for this disease and are strongly recommended in the acute phase. Your goal is to stop that inflammation in its tracks so that the patient doesn't progress to the chronic phase. Once they replace the muscle fibers with connective tissue, the game is over. The dog cannot open its mouth, chew, or be safely intubated or vomit. The chronic stage results in poor quality of life. Steroid protocols vary by neurologist. My protocol starts with 1 mg/kg PO q12h prednisone for 30 days, and then tapers slowly from there. Repeat 2M antibody titers every 1-2 months is recommended. Once the numbers return to normal, it is generally safe to stop the steroid administration.
If any dog has painful muscles of mastication, struggles to open its jaw without pain, and has an elevated CK on lab work a 2M antibody titer is recommended. Don't forget: neospora caninum and toxoplasma gondii can cause myositis and do attack the muscles of mastication. Concurrent testing for these two diseases in all dogs is strongly encouraged before starting immunosuppressive prednisone. I have been taken by surprise how often these tests are positive when I suspect this is "just" MMM.
Hopefully this helps you address muscle pain in your patients. If you have a question about a patient, please contact me via email or schedule a consultation online! Have a great week!
The Case of the Shrinking Head
Signalment: 4.5 year old MC Shepherd Mix
Clinical history: The dog had a 3 week history of left unilateral temporalis muscle atrophy when I met him. Hyporexia and nasal hemorrhage from the right nostril were noted when the signs first started, but they had improved by our consult. The atrophy, however, continued to progress.
Physical and Neurologic Examination:
The physical exam was normal.
Mentation: BAR
Cranial nerves: moderate left temporalis muscle atrophy, otherwise normal. No sensory abnormalities noted.
Gait: Ambulatory, no evidence of lameness, weakness or ataxia
Reflexes: normal all limbs
Postural reactions: Normal all limbs
Palpation: Non-painful spinal palpation and normal CROM
Neuroanatomic Lesion Localization?
Let's walk this through. First, what nerve innervates the temporalis muscles? (CN 5: trigeminal) So, our problem is a) peripheral trigeminal b) brainstem at the trigeminal motor nucleus or c) muscle. How do you sort between these? Right! Let's rule out the easy one first. Signs of brainstem disease include changes in mentation, paw replacement deficits (ipsilateral to the atrophy) and/or hemiparesis. Any one of these three abnormalities is present and voila! it is a brainstem lesion until otherwise discovered. We ruled out brainstem disease in this dog. Is this, then, peripheral trigeminal nerve (motor portion) or muscle? This differentiation can be hard on the neurologic examination so I actually included both of these possibilities on this dog's final neuroanatomic lesion localization. However, without a sensory deficit (he didn't have one) a trigeminal neuropathy is less likely. That said, if the CK is normal, it's hard to make a story for a myopathy. His was normal. So...I left both on the final list. You could have said "neuromuscular" and you would have been correct because that localization includes peripheral neuropathy, neuromuscular junction and myopathy.
Differential Diagnoses?
Neuropathy: Neoplasia, neuritis (infectious or non-infectious), hypothyroidism and trauma.
Myopathy: Masticatory muscle myositis (3M), infectious myositis (toxoplasma and Neospora caninum are most common causes of infectious myositis.)
Diagnostic Results
CBC, serum biochemistry: unremarkable.
T4: normal
Neospora antibody M titer: > 1:200 (positive!)
Toxoplasma IgG/IgM titer: Negative
3M antibody titer: < 1:100 (negative)
Conclusion
This patient was diagnosed with a Neospora myositis based on positive titers. We placed him on sulfa antibiotics and tracked the titers. Clindamycin is also an acceptable antibiotic choice for fighting protozoa myositis.
2 months later: 1:200
4 months later: 1:100
1.5 months later: negative.
Unfortunately, this patient developed an adverse reaction from the sulfa that included blood dyscrasias and hypothyroidism 5.5 months from the original diagnosis. The sulfa-based antibiotic was discontinued and clindamycin was started. My goal is to have 2 negative Neospora titers before discontinuing antibiotics but we will have to see if we get to meet that goal with this guy!
Key Points:
1. Muscle atrophy (especially unilateral) should prompt a toxoplasma (cat) and toxoplasma and Neospora titer (dog). This is a lesser known infection in Wisconsin dogs!
2. Treat with either a sulfa antibiotic or clindamycin to the point of two consecutive negative titers to ensure clearance of the infection. Titers are typically checked every 4-8 weeks.
This was a very interesting case and a great one to remind us all about protozoal infections in house pets. Remember - when we work together, we all learn!
I look forward to working with you soon.
Paroxysmal Dyskinesia
These words are not uttered by many of us on a regular basis (unless you are studying for boards and talking in your sleep). So, why do you need to know what this is? So that we remember that not all things that twitch have seizures.
Paroxysmal dyskinesia's are one, of a group, of movement disorders characterized by abnormal muscle movements UNRELATED to epileptic discharges. If you take one thing away from this email it is this: movement disorders are not seizures. Not that I suggest you stop reading...
How do I identify a Paroxysmal Dyskinesia (PD)?
This group of movement disorders manifest as sudden cramping in muscles and limbs. It has been identified in several breeds, with increased incidence in Terrier breeds. Notably there is no loss of consciousness, no autonomic signs, and upon recovery from the cramping the dogs return to normal function immediately. These cramping episodes can be triggered with specific activities in some patients (activity or exercise is a common trigger) and may last for minutes to hours. When performed, no EEG abnormalities consistent with epileptic discharges are noted.
What diagnostic testing should I run?
Cramping syndromes may be triggered from metabolic causes as well as genetic causes. A CBC, serum biochemistry and urinalysis are a wonderful way to rule out metabolic causes. If normal, assessment of a video can determine if additional testing for seizure disorder should be pursued.
Are there any treatment options?
Yes! Many movement disorders improve with anticonvulsant drugs such as the benzodiazepine class of drugs. One recent report (reference below) detailed successful treatment of a Welsh Terrier with levetiracetam (20 mg/kg PO q8h) to control signs.
Do you suspect you have a patient with a movement disorder? Please reach out for a consultation - I'm happy to help. I truly love working with you and your staff to help patients live their best lives, with neurologic disease. Keep up the good work!
Stay safe - it's almost spring time and we can make it!
Reference:
Green S, Olby N. Levetiracetam-responsive paroxysmal exertional dyskinesia in a Welsh Terrier. JVIM 2021: https://doi.org/10.1111/jvim.16068
