Myopathies - Proximal weakness without sensory involvement or UMN signs
Suggested examination:
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Perform a full neurological exam of the region in the prompt (e.g. upper limbs, lower limbs)
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If upper limbs and proximal weakness, then:
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Proceed to test fatiguability and cranial nerves ( such as eye movements, and lid lag) to help rule in or out NMJ disorders
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The salient features on examination were a symmetrical proximal weakness without sensory involvement or upper motor neuron signs, which I feel is most consistent with a myopathy, however there are other differentials, and I would like to discuss my findings in full.
In your discussion, you need to discuss the syndrome (proximal weakness), your differential for the neuroaxis (myopathy vs. NMJ vs. peripheral neuropathy), and then the underlying lesion/pathology for the one you consider most likely (e.g. differentials listed below for myopathy).
My differentials for proximal weakness include:
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Myopathic
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Inflammatory myopathies
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Polymyositis (anti-synthetases, anti-MDA5, anti-jo)
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Inclusion body (compared with PM, more likely to have distal and asymmetric involvement - Involvement of the hip flexors, quadriceps, tibialis anterior with weakness of the ankle dorsiflexors, and forearm flexors with grip weakness are characteristic of IBM)
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Anti-cN1A
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Immune mediated necrotizing myopathy
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Anti-HMGCR
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Other Acquired myopathies
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Inflammatory (above)
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Drug (steroids etc.) and alcohol
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Paraneoplastic
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Endocrine - thyroid, Cushing’s
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Hereditary muscular dystrophies - Becker’s, myotonic dystrophy, Limb girdle, facioscapulohumeral
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Neuromuscular junction disorders
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Anterior horn cell
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Motor neuron disease, and spinal muscular atrophy (Kugelberg-Welander disease [spinal muscular atrophy type 3] - proximal muscle wasting and fasciculation as a result of anterior horn cell damage).
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Non-length dependent peripheral neuropathy
I would like:
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CK and myositis antibodies
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EMG