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Diagnostic utility of a modified forearm ischemic exercise test and technical issues relevant to exercise testing
Mark Tarnopolsky1, Leslie Stevens, Jay R MacDonald
1Department of Neurology, McMaster University Medical Center, Room 4U4, 1200 Main Street W, Hamilton, Ontario L8N 3Z5, Canada. tarnopol@mcmaster.ca
Muscle & Nerve
|March 14, 2003
Summary
The modified forearm ischemic test (FIT) accurately diagnoses glycogen storage disease (GSD) and helps exclude myoadenylate deaminase deficiency (AMPD). However, FIT is not effective for diagnosing mitochondrial disease (MITO).
Area of Science:
- Clinical biochemistry
- Neuromuscular diagnostics
- Metabolic myopathies
Background:
- Accurate diagnosis of metabolic myopathies like glycogen storage disease (GSD), myoadenylate deaminase deficiency (AMPD), and mitochondrial disease (MITO) is crucial.
- The forearm ischemic test (FIT) is a diagnostic tool, but its modified application and diagnostic utility for specific conditions require evaluation.
- Understanding factors influencing FIT accuracy, such as catheter placement and pre-test diet, is important for reliable results.
Purpose of the Study:
- To determine the sensitivity and specificity of a modified forearm ischemic test (FIT) in diagnosing GSD, AMPD deficiency, and MITO disease.
- To assess the impact of catheter placement and antecedent sugar bolus on FIT results.
- To evaluate the diagnostic performance of FIT using muscle biopsy as a reference standard.
Main Methods:
- Retrospective review of FIT and muscle biopsy results from 99 patients with GSD, AMPD, MITO, other neuromuscular disorders, and controls.
- Analysis of FIT sensitivity and specificity for each condition.
- Assessment of catheter placement and pre-FIT sugar bolus effects in healthy individuals.
Main Results:
- Modified FIT demonstrated perfect sensitivity and specificity (1.00) for diagnosing GSD.
- FIT showed high sensitivity (1.00) but low specificity (0.37) for AMPD deficiency.
- A baseline lactate >2.5 mmol/L was specific (1.00) but not highly sensitive (0.62) for MITO disease. Optimal sensitivity/specificity for GSD and AMPD was achieved with baseline and +1 min samples. Incorrect catheter placement significantly attenuated lactate responses (P < 0.0001). Pre-FIT sugar bolus did not affect results.
Conclusions:
- A modified FIT is valuable for diagnosing GSD and excluding AMPD deficiency.
- The FIT is not a reliable diagnostic tool for MITO disease.
- Correct catheter placement is critical for accurate FIT interpretation; pre-test diet is less influential.