Brief Alerts
Modify the Ischemic Forearm Test
Source: Lindner A, et al. Neurology. 2001;56:1779-1780.
Serum lactate elevation normally occurs with exercise and absence of such elevation is the basis for the ischemic forearm test in the diagnosis of glycogen storage myopathies. Rarely, serious complications may result.
A 22-year-old woman with exertional cramps, weakness, and fatigue underwent the ischemic forearm test on the left forearm. Following 50 seconds of ischemic exercise with the left hand, she developed transient contracture followed by left forearm swelling, ulnar region hypesthesia, and elevated creatine kinase (3482 U/L, initially 815 u/L). Acute compartment syndrome was diagnosed and after fasciotomy she improved dramatically. Muscle biopsy subsequently revealed McArdle’s disease.
Commentary
Nonischemic forearm testing is a safe and reasonable alternative for detecting glycogen storage myopathy (Hogrel JY, et al. Neurology. 2001;56:1733-1738). Among 7 patients with myophosphorylase (n = 6) or debrancher (n =1) deficiency, no lactate elevation was seen, compared to 26 healthy controls where 4-fold elevation was produced. Nonischemic testing should replace the ischemic forearm testing if needed. Muscle biopsy or white blood cell enzyme assay remains the necessary and definitive diagnostic procedure in either case. —Michael Rubin
Sjogren’s Syndrome and the Peripheral Nervous System
Source: Barendregt PJ, et al. Ann Rheum Dis. 2001;60:876-881.
Among 39 patients with primary Sjogren’s syndrome (SS) diagnosed by positive serology (at least 1 positive test among antinuclear, rheumatoid factor, SS-A, or SS-B antibodies) and positive salivary gland biopsy or sialography, evidence for peripheral nervous system (PNS) involvement was sought using clinical and electrodiagnostic means. Concomitant diseases affecting the PNS were excluded, including diabetes and renal failure, as were a history of drug use known to cause neuropathy. All patients underwent neurological examination with particular attention to the PNS. Electrodiagnostic studies included routine nerve conduction studies and quantitative sensory testing encompassing vibration detection threshold, and warm and cold sensitivity (temperature discrimination threshold). Autonomic studies comprised cardiovascular function tests using tilt-table testing with blood pressure and heart rate measurements, beat-to-beat variability on Valsalva maneuver, and pupillography. Wilcoxon testing and Pearson’s correlation coefficient provided statistical analysis.
Commentary
Although no patients had spontaneous neurological complaints, 8 (one fifth) answered positively on detailed questioning for neuropathic symptoms. Of these, 6 demonstrated abnormalities on examination, 5 on vibration detection threshold, 4 on nerve conduction studies, 3 on cold sensitivity, and 2 on warm sensitivity. Seven (18%) patients had an abnormal neurological examination, 3 showing vibration detection threshold abnormalities, and 3 and 2 cold and warm sensitivity abnormalities, respectively. Overall, 58% (22/38) had abnormal vibration detection threshold, 20% (7/35) and 14% (5/35) had warm and cold sensitivity abnormalities, and 23% (9/39) had nerve conduction studies consistent with polyneuropathy, either motor, sensory, or mixed. Vibration detection abnormalities did not correlate with temperature discrimination threshold abnormalities, nor did autonomic abnormalities correlate with each other or with other electrodiagnostic studies. Subclinical involvement of the PNS is common in asymptomatic patients with primary SS. —Michael Rubin
Rubin, MD, Associate Professor, Clinical Neurology, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.
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