Investigations
1st investigations to order
polysomnography: electromyography (EMG) evaluation of limb movements
Test
Surface EMG is recorded over the tibialis anterior muscles. Movements include a tonic activity lasting several hundreds of milliseconds, which may be followed by myoclonic activity; an initial myoclonic jerk, followed by tonic activity; or several myoclonic jerks in clusters (polymyoclonus), sometimes followed by tonic activity.
World Association of Sleep Medicine (WASM) 2016 standards for recording and scoring leg movements in polysomnograms define candidate leg movements (CLM) as any monolateral leg movements lasting 0.5 to 10 seconds or bilateral leg movements lasting 0.5 to 15 seconds. Periodic leg movements (PLM) are defined by runs of at least four consecutive CLM with an intermovement interval ≥10 and ≤90 seconds without any CLM preceded by an interval <10 seconds interrupting the PLM series.[3]
Result
periodic limb movements of sleep (PLMS) index (number of PLMS per hour of total sleep time) >15 for the whole night is pathological
polysomnography: electroencephalogram (EEG) evaluation
Test
EEG recording in polysomnography is performed with 2 'reference' electrodes and 6 'exploring' electrodes attached with paste to the scalp over the frontal, central, and occipital areas.[27] Recordings from these electrodes can be grouped into different stages of sleep (non-REM, stages 1 to 4, and REM sleep) and wakefulness.
Result
PLMS predominantly during non-rapid eye movement (REM) stages 1 and 2 of sleep, and progressively diminishing during deep sleep stages 3 to 4
polysomnography: assessment of sleep-related breathing disorders
Test
PLMS may be associated with sleep-related breathing disorders, such as obstructive sleep apnoea.[1] Movements may occur in close temporal association with apnoeas or independently from apnoeic episodes. Apnoeas and hypopnoeas should be scored.[27]
Evaluation of respiratory disorders is important, as these may independently be the cause of sleep disturbances, and may be amenable to treatment with non-invasive ventilation techniques.
Result
breathing irregularities such as apnoeas and hypopnoeas in sleep-related breathing disorders
FBC
Test
Should be requested to exclude iron deficiency anaemia, which may be associated with PLMD. This finding; however, is very non-specific, and iron replacement may not result in resolution of symptoms.
Result
may reveal anaemia
serum ferritin
Test
Should be requested to exclude iron deficiency. This finding; however, is very non-specific and iron replacement may not result in resolution of symptoms.
Standard diagnostic criteria have not been defined; however, many recommend iron supplementation if serum ferritin is <101 pmol/L (<45 micrograms/L or 45 nanograms/mL).[28]
Result
low in iron deficiency anaemia
urea
Test
Uraemia in end-stage renal failure may result in PLMD.
Result
uraemia in end-stage renal failure
Investigations to consider
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