The "spray can" sign: validation of a clinical observation in chronic inflammatory demyelinating polyneuropathy.

BACKGROUND The presentation of chronic inflammatory neuropathies is variable. The decision regarding when to intervene with treatment is ideally determined by identifying early markers of loss of function. OBJECTIVE To test the hypothesis that an observation of functional impairment, defined by a patient with demyelinating neuropathy, can be used as a reproducible and reliable measure of improvement with intravenous immune globulin. DESIGN A 28-year-old woman presented with a chronic inflammatory demyelinating polyneuropathy. Her first complaint was the inability to use her deodorant spray because of hand weakness. A calibrated pincer gauge fixed on top of her usual spray can was used to objectively test finger flexion. Tip grip and lateral pinch were also measured. A calibrated dynamometer was used to measure grip strength. RESULTS Power and precision grip force were reproducible in normal control subjects by means of the spray can test. This test proved to be a reliable indicator of reduced muscle strength in the patient and improved after treatment with intravenous immune globulin. CONCLUSIONS The spray can test objectively quantified the daily function, nominated by the patient, of operating an aerosol can. This measurement, drawn from a functional loss observed by the patient, proved to be a portable and reliable indicator of decline and recovery in chronic inflammatory demyelinating polyneuropathy.