Difference between neuropathy n mypathy

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Now I have excellent textbook content from Harrison's 22nd Edition and Bradley & Daroff's Neurology. Here is a thorough, well-sourced comparison:

Neuropathy vs. Myopathy

These are two distinct categories of neuromuscular disease. Neuropathy affects the peripheral nerves, while myopathy affects the muscles themselves.

1. Definition and Site of Lesion

Feature	Neuropathy	Myopathy
Site	Peripheral nerve (axon, myelin, or cell body)	Muscle fiber (structural or functional)
Part of motor unit affected	Lower motor neuron / peripheral nerve	Muscle (end-organ)

Neuropathy: "Peripheral nerves are composed of sensory, motor, and autonomic elements. Diseases can affect the cell body of a neuron or its peripheral processes, namely the axons or the encasing myelin sheaths." - Harrison's Principles of Internal Medicine, 22nd Ed.
Myopathy: "Myopathies are disorders with structural changes or functional impairment of muscle and can be differentiated from other diseases of the motor unit (e.g., lower motor neuron or neuromuscular junction pathologies) by characteristic clinical and laboratory findings." - Harrison's Principles of Internal Medicine, 22nd Ed.

2. Pattern of Weakness

Feature	Neuropathy	Myopathy
Distribution	Typically distal (glove-and-stocking)	Typically proximal (limb-girdle: shoulders, hips)
Symmetry	Symmetric or asymmetric depending on type	Usually symmetric
Onset	Often distal extremities first	Shoulder girdle, pelvic girdle first

In neuropathy, the distribution of weakness is key - symmetric proximal and distal weakness suggests acquired demyelinating polyneuropathy (e.g., GBS, CIDP), while distal-only weakness suggests axonal neuropathy. In myopathy, proximal weakness (difficulty climbing stairs, rising from a chair, raising arms overhead) is the hallmark.

3. Sensory Involvement

Feature	Neuropathy	Myopathy
Sensation	Often impaired (pain, temperature, vibration, proprioception)	Normal - sensation is preserved
Sensory symptoms	Numbness, tingling, burning, pain	Absent

"An associated sensory loss suggests a peripheral neuropathy or a CNS abnormality (e.g., myelopathy) rather than a myopathy." - Harrison's Principles of Internal Medicine, 22nd Ed.

4. Reflexes

Feature	Neuropathy	Myopathy
Deep tendon reflexes (DTRs)	Reduced or absent (especially ankle jerk)	Preserved until late/severe disease

Loss of reflexes (areflexia) alongside distal weakness and sensory loss strongly suggests neuropathy.

5. Autonomic Involvement

Feature	Neuropathy	Myopathy
Autonomic dysfunction	Common in some types (orthostatic hypotension, bowel/bladder, sweating)	Absent

Autonomic dysfunction in the absence of diabetes should raise suspicion for amyloid polyneuropathy specifically.

6. Additional Symptoms

Feature	Neuropathy	Myopathy
Muscle cramps	Common (motor neuron disease, polyneuropathy)	Not typical in primary myopathy
Muscle pain (myalgia)	Less prominent	Can occur (inflammatory myopathies, metabolic)
Fasciculations	Present (esp. motor neuron disease)	Absent
Muscle atrophy	Late, neurogenic (angular atrophy on biopsy)	Can occur late; rounded fibers

7. Investigations

Investigation	Neuropathy	Myopathy
Serum CK (creatine kinase)	Normal or mildly elevated	Often markedly elevated (>1000 IU/L in inflammatory or dystrophic myopathies)
Nerve conduction studies (NCS)	Abnormal - reduced velocity (demyelinating) or reduced amplitude (axonal)	Normal nerve conduction
EMG	Fibrillations, positive sharp waves, large MUAPs, reduced recruitment	Small, short, polyphasic MUAPs ("myopathic pattern"); early recruitment
Muscle biopsy	Grouped atrophy (neurogenic)	Myopathic changes: necrosis, regeneration, inflammation, structural changes
Nerve biopsy	May show axonal loss, demyelination, inflammation	Normal

8. Sub-classification

Neuropathy types (based on what's affected):

Axonopathy - axon degeneration (e.g., diabetic neuropathy, alcohol)
Myelinopathy - myelin damage (e.g., GBS, CIDP, Charcot-Marie-Tooth)
Neuronopathy/ganglionopathy - cell body (e.g., paraneoplastic)
Autonomic neuropathy - autonomic fibers

Myopathy types:

Muscular dystrophies (e.g., Duchenne, Becker, limb-girdle)
Inflammatory myopathies (polymyositis, dermatomyositis, inclusion body myositis)
Metabolic myopathies (glycogen, lipid storage disorders)
Mitochondrial myopathies
Toxic myopathies (statins, alcohol, steroids)
Endocrine myopathies (hypothyroid, Cushing's)
Congenital myopathies (central core, nemaline rod)

9. Quick Summary Table

Feature	Neuropathy	Myopathy
Site	Peripheral nerve	Muscle
Weakness pattern	Distal > proximal	Proximal > distal
Sensation	Impaired	Normal
Reflexes	Reduced/absent	Preserved (until late)
Autonomic symptoms	Present in some	Absent
Serum CK	Normal/mild	Elevated (often markedly)
NCS	Abnormal	Normal
EMG	Neurogenic pattern	Myopathic pattern
Biopsy	Grouped/angular atrophy	Myopathic changes
Examples	Diabetic neuropathy, GBS, CMT	Polymyositis, DMD, statin myopathy

Sources: Harrison's Principles of Internal Medicine, 22nd Ed. (Chapters 457 & 460 - Peripheral Neuropathy and Myopathy); Bradley and Daroff's Neurology in Clinical Practice

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