This patient is an elderly man with restless legs, unintentional weight loss, and pale sclerae on exam, most likely due to iron deficiency anemia (IDA) resulting in restless leg syndrome (RLS). Colorectal cancer is high on the differential and should be ruled out with a colonoscopy.
This patient’s symptoms are highly consistent with RLS: night awakening due to urges to move legs, restless legs with inactivity before bed, and alleviation of symptoms by movement or massage. RLS can be due to IDA (iron is a cofactor for dopamine synthesis) or other dopaminergic causes that are currently less clearly defined. In this patient with scleral pallor and unintentional weight loss, IDA is more likely. Iron studies would be expected to reveal low ferritin and high total iron binding capacity. For an elderly person with an unknown cause of IDA, especially without a recent colonoscopy, workup for colorectal cancer is indicated. Although colorectal cancer may present with abdominal discomfort, melena or hematochezia, and changes in stool, it is often largely asymptomatic, as in this patient. Failure to identify the underlying cause of IDA/RLS in this patient could not only make treatment (such as iron supplementation or pramipexole) ineffective but also delay the diagnosis of a potentially fatal condition.
Illustration A shows a Dopamine uptake scan (DaTscan) in a normal person on the left and a patient with Parkinson's disease (PD) on the right. In the latter, there is asymmetrically decreased dopamine uptake in the basal ganglia.
Answer 1: DaTscan of the brain is a study that uses ioflupane I-123 to detect dopamine uptake in the basal ganglia (Illustration A) and can be used for PD as a supplement to clinical diagnosis. Although patients with PD may also have restless legs, their presentation tends to be intermittent and less severe, unlike this patient’s progressive and chronic symptoms. Furthermore, this patient does not have any other signs or symptoms of PD (bradykinesia or resting tremor). The DaTscan would therefore be unhelpful for this patient.
Answer 2: A trial of iron supplementation can help alleviate RLS symptoms if IDA with ferritin < 75 ng/mL is the underlying cause. However, doing so without first performing iron studies would be inappropriate, as it may cause iron overload in those with undiagnosed hemochromatosis. Furthermore, the underlying cause of this patient's IDA is likely colon cancer, and establishing the presence of malignancy is paramount before supplementation.
Answer 4: A trial of reduction in caffeine intake may help slightly in patients with RLS, but it would not reveal an underlying cause since caffeine is not directly causative of RLS. In addition, although he has increased his coffee consumption, he is still under the general daily limit of 400 mg of caffeine (with approximately 100 mg in each cup of coffee).
Answer 5: A trial of pramipexole may be helpful in identifying idiopathic RLS, since pramipexole is a dopamine agonist that can be used to treat RLS not due to IDA. Of note, even in patients whose RLS is not due to IDA, nonpharmacologic strategies such as regular exercise and pneumatic compression are recommended before turning to medications.
Restless leg syndrome presents with an unpleasant urge to move one’s legs during inactivity or sleep; and movement or massage may help relieve symptoms. Iron deficiency anemia is a known cause of this condition, and in a patient with risk factors for colorectal cancer, colonoscopy should be performed to evaluate for a cause of blood loss.