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.
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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