Hyporeflexia is a diminution of tendon reflexes, short of their total absence (areflexia). This may be physiological, as with the diminution of the ankle jerks with normal ageing; or pathological, most usually as a feature of peripheral lesions, such as radiculopathy or neuropathy. The latter may be axonal or demyelinating, in the latter the blunting of the reflex may be out of proportion to associated weakness or sensory loss. Although frequently characterized as a feature of the lower motor neurone syndrome, the pathology underlying hyporeflexia may occur anywhere along the monosynaptic reflex arc, including the sensory afferent fibre and dorsal root ganglion as well as the motor efferent fibre, and/or the spinal cord synapse.
Hyporeflexia may also accompany central lesions, particularly with involvement of the mesencephalic and upper pontine reticular formation. Hyporeflexia is an accompaniment of hemiballismus, and may also be noted in brainstem encephalitis (Bickerstaff ’s encephalitis), in which the presence of a peripheral nerve disorder is debated. Hyporeflexia is not a feature of myasthenia gravis but may occur in Lambert-Eaton myasthenic syndrome (cf. facilitation); it is not seen in most muscle diseases unless they are advanced.