Correct!
2. Ferritin level of 18 ng/ml
Ms. Jones’ symptoms are highly suggestive of restless legs syndrome (RLS). Low peripheral iron stores defined as serum ferritin < 45 – 50 ng/ml despite being in the “normal range” has been associated with RLS. Iron deficiency is a well-defined environmental factor in RLS. Low cerebrospinal fluid (CSF) ferritin levels have also been demonstrated in RLS patients even with normal serum ferritin levels (1). Iron is an essential cofactor for tyrosine hydroxylase, which is a rate-limiting step in the conversion of levodopa to dopamine (2). Therefore, a decrease in iron may affect the availability of dopamine which is a neurotransmitter implicated in the pathophysiology of RLS. There is a circadian variation in the availability of iron and the activity of tyrosine hydroxylase, thus corresponding with the nighttime occurrence/aggravation of RLS symptoms (3). Conditions that decrease iron availability (pregnancy, end stage renal disease) demonstrate an increased prevalence of RLS.
Her TSH of 6 mIU/ml is mildly elevated and is unlikely to cause symptoms. While hypothyroidism may present with symptoms of neuropathy and myopathy, which may mimic RLS, symptoms do not demonstrate a marked circadian variation or relationship to sedentary activities (i.e. they do not typically occur only at rest and are not as noticeably alleviated by movement).
Increase in serum bicarbonate levels to the upper limits of normal or above, may be seen in hypoventilation syndromes and may be associated with daytime fatigue however this does not explain the predominantly sensory symptoms described by the patient.
RLS is a clinical diagnosis and does not require a polysomnogram for diagnosis. The revised diagnostic criteria for diagnosis of RLS set forth by the International Restless Legs Study Group (IRLSSG) in 2012 consists of four clinical criteria, and three supportive criteria (2). The presence of PLMs on polysomnography corroborates the diagnosis of RLS especially when there is doubt, but it is not an essential diagnostic criterion. Moreover, only 80% of patients with RLS have PLMs on polysomnographic monitoring.
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