7yo Golden with progressive hindlimb weakness, elevated C...

Thanks for reaching out. This is a classic presentation where we need to be systematic to avoid getting led astray. The elevated CK is a critical clue, but it doesn't give us the address of the problem. It tells us there's muscle damage, but it doesn't tell us if the muscle itself is the primary issue (myopathy) or if it's suffering because of a nerve problem (neuropathy/myelopathy).

Our first and most important job is to neurolocalize. The physical examination will be our highest-yield diagnostic test here. I need you to focus on a few key things for me:

Spinal Reflexes: Check the patellar and withdrawal reflexes in the pelvic limbs. Are they normal, increased (brisk/clonus), or decreased/absent? This is the crucial step in differentiating an upper motor neuron (UMN) lesion in the T3-L3 spine from a lower motor neuron (LMN) lesion in the L4-S3 segments or peripheral nerves/muscles.

Proprioception: How is conscious proprioception (knuckling) in the hind limbs? Is it absent, delayed, or normal? Check the front limbs as well to confirm the problem is localized to the rear.

Pain Perception: Is there any spinal hyperesthesia on palpation, specifically over the thoracolumbar or lumbosacral regions?

Muscle Tone & Atrophy: Assess the muscle tone in the hindlimbs. Is it firm and spastic (UMN) or flaccid (LMN)? Is there significant, rapid-onset muscle atrophy?

If you find UMN signs (brisk reflexes, normal to increased tone) in the hindlimbs, we're likely looking at a T3-L3 myelopathy (e.g., chronic IVDD, spinal neoplasia, degenerative myelopathy). The elevated CK in this case would be secondary to disuse or nerve root signature.

If you find LMN signs (decreased/absent reflexes, flaccid tone), our lesion is in the L4-S3 region or is a diffuse neuromuscular issue. This is where differentials like lumbosacral stenosis, polyradiculoneuritis, or a primary polymyositis come into play, and the CK becomes a more direct clue.

Elena, from your perspective in Internal Medicine, could you please weigh in on the initial bloodwork? I'd be interested in other metabolic causes of weakness and whether you see any patterns suggestive of a systemic inflammatory or infectious process that could cause a primary myositis.

Let's start with that detailed neuro exam, and we'll build our diagnostic plan from there.

David will be essential for localizing the neurologic component of the weakness, so I'll focus on the systemic and primary muscle diseases suggested by the elevated CK. That lab value is our strongest clue and points us directly toward myocyte injury.

My differential list for a middle-aged Golden with hindlimb weakness and elevated CK, from a medical perspective, is prioritized as follows:

Immune-Mediated Polymyositis (IMP): This is an inflammatory condition where the immune system attacks the muscles. It fits the presentation well and can cause profound weakness, muscle pain, and very high CK levels. It can be a primary disease or secondary to an underlying trigger.

Paraneoplastic Syndrome: In a 7-year-old Golden, we must consider that an occult tumor (like lymphoma or hemangiosarcoma) is triggering a secondary myositis. The muscle disease is a symptom of the cancer.

Infectious Myositis: We need to rule out infectious triggers, primarily tick-borne diseases (Ehrlichia, Anaplasma, RMSF) and protozoal infections (Neospora, Toxoplasma), which can all cause systemic inflammation with muscle involvement.

Endocrine Myopathy: Hypothyroidism is a classic "don't miss" differential. It's common in this breed and can cause weakness, lethargy, and mild to moderate CK elevation. It's less likely to cause a dramatically high CK, but it must be ruled out.

My Proposed Diagnostic Plan:

While David conducts his neurologic exam, I would proceed with the following to investigate the systemic causes:

* Minimum Database: A full CBC, chemistry panel, and urinalysis to assess overall health, electrolytes, and look for concurrent organ involvement.
Infectious Disease Screening: A comprehensive tick-borne disease panel (serology and PCR). Serology for Neospora and Toxoplasma*.
* Endocrine Testing: A full thyroid panel including a T4, free T4 by equilibrium dialysis, and a TSH. A baseline cortisol is a simple, effective screen to rule out hypoadrenocorticism.
* Neoplasia Screening: Three-view thoracic radiographs and a thorough abdominal ultrasound are non-negotiable in this signalment to search for primary neoplasia.

If this initial workup is unrewarding, the definitive diagnostic step for a primary myopathy is a muscle biopsy for histopathology. This would confirm inflammation and help differentiate IMP from other, rarer myopathies.

This is a classic "neuro-medical" crossover case. My workup can proceed in parallel with David's to efficiently rule systemic disease in or out.

Confidence: High confidence that a systemic medical condition is a primary differential.