Sympathetic skin response in monomelic amyotrophy

Area of Science:

• Neurology
• Autonomic Nervous System Research
• Motor Neuron Disease Studies

Background:

• Monomelic amyotrophy (MMA) is a motor neuron disease variant characterized by limb-specific weakness and atrophy.
• Some MMA patients exhibit symptoms like increased sweating and cyanosis, suggesting potential autonomic nervous system involvement.
• The benign prognosis of MMA contrasts with the observed autonomic symptoms in some cases.

Purpose of the Study:

• To investigate the involvement of the sympathetic nervous system in Monomelic Amyotrophy (MMA).
• To quantify sympathetic nervous system function using sympathetic skin response (SSR) measurements in MMA patients.
• To compare SSR parameters between affected limbs, unaffected limbs, and healthy controls.

Main Methods:

• Electromyography and nerve conduction studies were performed on 9 MMA patients with upper limb atrophy.
• Sympathetic skin response (SSR) was recorded in all four limbs of patients and 25 age-matched healthy controls.
• Stimulation at Erb's point and around the elbow was used to assess for conduction blocks.

Main Results:

• Mean SSR latency was significantly prolonged in the affected upper limbs of MMA patients compared to controls (P=0.03).
• SSR latency was also prolonged in both atrophied and clinically normal upper limbs of patients (P=0.05).
• No significant differences in SSR latency were found in the lower limbs of patients compared to controls (P=0.09).

Conclusions:

• The sympathetic nervous system is implicated in Monomelic Amyotrophy, affecting both the atrophic and clinically unaffected upper limbs.
• These findings suggest a more widespread sympathetic nervous system dysfunction in MMA than previously recognized.
• The lower limbs do not appear to be significantly involved in the sympathetic nervous system dysfunction observed in MMA.