Relationships Between Clinical Symptom Severity Scales and Nerve Conduction Measures in Carpal Tunnel Syndrome.

You H, Simmons Z, Freivalds A, et al (Department of Industrial and Manufacturing Engineering, The Pennsylvania State University, University Park, Pa; Division of Neurology and Department of Orthopedics and Rehabilitation, The Pennsylvania State University College of Medicine, Milton S Hershey Medical Center, Hershey, Pa), Muscle Nerve. 1999;22:497-501.

The purpose of this study was to investigate the relationship between a clinical symptom survey and the electrodiagnostic measurements commonly used in the diagnosis of carpal tunnel syndrome (CTS).

Subjects were recruited from patients at an electromyography laboratory who were diagnosed with unilateral or bilateral CTS. Additional inclusion criteria included pain, weakness, numbness, or tingling in the symptomatic extremity; age greater than 18 years; employment at the time of participation; working at their job for at least 1 year; and no surgery for CTS on the involved limb. The researchers evaluated 64 hands of 45 patients (11 men, 34 women) with CTS. The subjects had an average age of 46.7 years (SD=10.2, range=24-65 years).

Electrodiagnostic testing for CTS included nerve conduction studies using supramaximal percutaneous electrical nerve stimulation and surface electrode recording, which obtained motor and sensory responses. In this study, carpal tunnel syndrome was defined as being present if ulnar nerve electrodiagnostic studies were normal and if median nerve studies documented a distal peak latency of the sensory nerve action potential greater than 3.7 m/s, a distal onset latency of the compound muscle action potential greater than 4.4 m/s, or a conduction velocity of the sensory nerve fibers of less than 49 m/s.

Immediately following their electrodiagnostic tests, the subjects completed a symptom severity questionnaire. The questions evaluated the magnitude, frequency, and duration of 6 typical CTS symptoms: pain, weakness, clumsiness, numbness, tingling, and nocturnal symptoms.

Pearson product moment correlation analysis was used to assess the relationships between the questionnaire responses and electrodiagnostic measures. Factor analysis was used to determine the relationships among the symptoms included in the survey.

Factor analysis revealed that the 6 clinical scales could be divided into 2 groups of symptoms: a primary group that consisted of numbness, tingling, and nocturnal symptoms and a secondary group that consisted of pain, weakness, and clumsiness. In addition, all nerve conduction measures were significantly interrelated to each other. The strongest correlation was between sensory peak latency and motor onset latency. Low correlations were found between motor amplitude and the other nerve conduction measures (ie, sensory conduction velocity, distal peak sensory latency, sensory amplitude). Pearson product moment correlation coefficients were significant between the primary symptom group and all nerve conduction measures except the motor amplitude measure. The overall (combined) symptom scales were also significant in a similar pattern. Secondary symptom scales were significantly correlated to distal latency of the sensory nerve, conduction velocity of the sensory nerve, and distal latency of the motor nerve. Correlations with the nerve conduction measures, however, were generally strongest for the primary symptom group compared with the secondary or overall (combined) group of symptoms.

The authors concluded that a dichotomous classification scheme for symptoms of CTS is necessary. Because the severity of primary symptoms was more closely related to nerve conduction measures than secondary symptoms, the authors believed that a separation of the symptoms in a symptom assessment tool is more likely to have biological significance and to reflect median nerve injury.

Nancy R Talbott, PT
University of Cincinnati
Cincinnati, Ohio