1. The lack of atrophy in a weak muscle indicates either an upper motor neuron lesion or purely demyelinating lesion and may represent spurious weakness.
2. The lack of weakness may be due to confusion, inattention, uncooperativeness, PAIN, feigning or a somatization disorder.
3. Fasciculations may be present in radiculopathies or other focal neuropathies as well as in disorders of the anterior horn.
4. Examination of the tendon reflexes is more objective than muscle power or sensory testing.
Sensory testing pearls:
1. Hyperesthesia, allodynia or hyperpathia are possible as well as hypesthesia.
2. The distribution of sensory loss is usually partial, often in the distal part of the dermatome,eg. the fingertips only in carpal tunnel syndrome. This may be due to damage only to selected fascicles within a proximal part of the nerve (ie. the lesion need not be distal).
Anatomic pitfalls: dermatome and myotome variations
1. Tibialis anterior, in root stimulation studies, is innervated by L4 75 % of the time, not L5.
2. EDB (in foot) can be L5 or S1 even more variably.
3. Dermatomal maps are based on flimsy anatomic evidence.
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