Are sensory deficits more common than motor deficits in Distal Symmetric Polyneuropathy (DSP)?

Sensory Deficits Are More Common Than Motor Deficits in Distal Symmetric Polyneuropathy (DSP)

Yes, sensory deficits are significantly more common than motor deficits in distal symmetric polyneuropathy (DSP), with sensory symptoms typically predominating in the clinical presentation. 1

Clinical Presentation of DSP

Sensory Manifestations

• DSP is characterized by length-dependent, sensory-predominant symptoms and signs, including potentially disabling symmetric chronic pain, tingling, and poor balance 1
• Symptoms typically begin symmetrically in the toes and feet, later progressing to fingertips as the condition advances in a length-dependent pattern 2
• Patients experience distal paresthesia, hyperesthesia, numbness, and sensory loss that affects the feet more than the hands 3
• Sensory symptoms commonly include:
  • Pain and positive sensory symptoms in a stocking-and-glove distribution 3
  • Changes in proprioception and vibratory sensitivity 3
  • Elevated touch detection threshold and impaired sharpness detection 3

Motor Involvement

• Motor impairment is relatively rare compared to sensory deficits in DSP 3
• When present, motor symptoms typically consist of mild to severe distal weakness in the lower limbs, occurring in approximately 10% of patients 3
• Motor nerve involvement is often a later manifestation after sensory symptoms have become established 3

Evidence from Specific Neuropathy Types

Small Fiber Polyneuropathy

• Small fiber polyneuropathy, a common subtype of DSP, presents with prominent pain and autonomic symptoms with minimal or absent motor findings 2
• Skin biopsy with intraepidermal nerve fiber (IENF) density assessment is a validated marker of small fiber sensory pathology, highlighting the predominance of sensory involvement 3
• IENF are the nerve terminals of somatic unmyelinated C fibers, which are predominantly affected in small fiber sensory neuropathy (SFSN) 3

Medication-Induced Neuropathies

• Bortezomib-induced peripheral neuropathy is predominantly sensory rather than motor, affecting all fiber types in sensory nerves 3
• Thalidomide-induced neuropathy manifests primarily with bilateral and symmetrical sensory disorders, with motor disorders being rare 3
• Electrophysiological studies of these medication-induced neuropathies reveal predominantly low amplitude of sensory action potentials, consistent with a length-dependent, sensory, axonal polyneuropathy 3

Diagnostic Considerations

Physical Examination Findings

• Physical examination in DSP typically reveals distal sensory loss, reduced or absent reflexes, and sometimes distal muscle weakness 2
• The most common neurologic examination items included in DSP assessment scales are:
  • Vibration perception (100% of scales)
  • Reflexes (89% of scales)
  • Pinprick perception (78% of scales)
  • Muscle strength (61% of scales)
  • Touch-pressure perception (50% of scales)
  • Joint position perception (44% of scales) 4
• This distribution of examination items in assessment scales reflects the predominance of sensory over motor findings in DSP 4

Autonomic Involvement

• Autonomic symptoms may also be present in DSP, including orthostatic hypotension, alternating diarrhea and constipation, urinary retention, and sexual dysfunction 2
• Orthostatic hypotension has been reported in about 10% of patients with certain types of medication-induced DSP 3
• Autonomic testing can document autonomic system dysfunction in polyneuropathy, which is particularly relevant to small fiber polyneuropathy 3

Clinical Implications

• The sensory-predominant nature of DSP has important implications for diagnosis and management 1
• Standardizing DSP metrics, as already accomplished for motor neuropathies, would permit better in-clinic longitudinal tracking of natural history and treatment responses 1
• The predominance of sensory symptoms means that pain management is often a primary focus of treatment, with management changes related to neuropathic pain being common (48.9% of cases in one study) 5
• Diagnostic testing should focus on identifying potentially treatable causes of DSP, with inexpensive blood tests for diabetes, thyroid dysfunction, and vitamin B12 deficiency allowing for identification of new causes in 15.5% of patients in one study 5