Chronic Neuropathies

Clinical signs associated with chronic neuropathy consist of tetraparesis with hypotonia to atonia, hyporeflexia to areflexia, denervation atrophy, +/- ataxia (CP deficits), and +/- sensory impairment. Bladder control & panniculus are often intact and pain sensation is often spared.

Diagnostic Plan

Once a polyneuropathy is suspected, I work through my diagnostic plan in tiers of increasing complexity to try to determine the etiology of the peripheral nerve disease. Despite full evaluation, as many as 50% of dogs remain undiagnosed or return with a diagnosis of chronic axonal degeneration. The initial tier of diagnostic tests consists of primarily bloodwork to assess metabolic and endocrine function as well as to look for infectious disease. The initial testing would comprise a CBC and biochemistry panel, free T4 and endogenous TSH, a low dose dexamethasone suppression test or ACTH stimulation test with endogenous ACTH, ANA, FeLV and FIV titers (cats), Neospora caninum titer (dogs) +/- Toxoplasma titer (cats and dogs), +/- AchE level.

The second tier of diagnostic evaluation is primarily associated with evaluation for possible neoplasia. Testing will include radiography of thorax and abdomen, abdominal ultrasound and CSF analysis.

If all of the above diagnostic tests are negative or normal, further evaluation of the type of generalized nerve disease should be evaluated via electrophysiology. The two main categories of peripheral nerve pathology are demyelination and axonal disease. However, many dogs have a combination of the above changes. Electrophysiology also reveals the relative distribution of the neuropathy both in location along the length of the nerves and degree of severity. Electrophysiology testing would consist of EMG, motor and sensory nerve conduction velocities, CMAP and SNAP amplitudes, supramaximal repetitive stimulation, dorsal and ventral nerve root studies. Normal muscle is electrically silent on electromyography. EMG will assist in assessing the presence of denervation and therefore axonopathy and the degree of severity of the changes. Purely demyelinating neuropathies will produce very little in the way of EMG abnormalities. EMG also helps determines whether observed muscle atrophy is due to denervation or disuse. Electrophysiology also helps differentiates between peripheral nerve, muscle and n-m junction diseases. Based on the electrodiagnostic evaluation, the next important step in nerve and muscle evaluation is fascicular nerve biopsy (commonly of the distal tibial or common peroneal nerve) and muscle biopsy (often distal appendicular muscles). [...]