Correspondence Address:
Dr. Manjari Tripathi
Department of Neurology, Neurosciences Centre, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029
India

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Periodic limb movement disorder (PLMD) is defined as the occurrence of periodic episodes of repetitive and highly stereotyped limb movements during sleep. Many secondary causes of PLMD such as age, narcolepsy, uremia, polyneuropathy, anemia, and pregnancy have been reported in literature.[1],[2],[3],[4] To the best of our knowledge, this is the first reported case of PLMD secondary to insulinoma.

A 54-year-old woman presented to the neurology clinic with a 5-year history of having episodes of repetitive leg movements during sleep occurring once or twice a week. She had no recall of these episodes, and these episodes were noticed by her husband. Relatives also noticed that since last 6 months she had abnormal behavior in the morning with incoherent speech, confusion, and sweating. They also noticed that during days when she used to fast for religious purposes her emotional responses were inappropriate. The affect and response time used to improve after having tea with unrefined sugar. She had no personal or family history of diabetes mellitus, and was not taking any oral hypoglycemic drugs. For these episodes, she was also given a trial of antiepileptic drugs but no improvement was observed.

Neurological examination was within normal limits. Complete blood count, electrolytes, renal function tests, liver function tests, and random blood sugar levels were normal. No abnormalities were observed on brain magnetic resonance imaging (MRI) and interictal electroencephalogram (EEG).

A working diagnosis of seizure was kept, and the patient was admitted and connected to video EEG to record these habitual episodes. Around 3h after the onset of sleep, the patient had abnormal rhythmic movements of both legs with flexion at the hip and knee, and extension of the ankle and toes, lasting for 5–15s [Video 1]. On reviewing the EEG, no epileptiform wave forms were observed during this episode. But there was slowing in background activity, followed by the appearance of generalized theta/delta activity that lasted for 30s. Blood sugar level measured during the episode by glucometer was 24mg/dL. To get more details regarding this episode during sleep, a video-polysomnography (PSG) monitoring in the sleep laboratory was performed.

[MULTIMEDIA:1]

PSG [Figure 1] showed evidence of periodic limb movements in the form of a phasic increase in electromyography (EMG) amplitude in the lower limb channel, lasting for 4–6s at intervals of 5–10s.{Figure 1}

On evaluating the cause of these unprovoked hypoglycemic episodes, it was found that they were accompanied with an inappropriately high insulin level with elevated C-peptide levels, suggesting an endogenous source. Multiphasic computed tomography and MRI of abdomen revealed an arterial-enhancing lesion in the body of pancreas, which was removed surgically. Histopathology confirmed the lesion to be an insulinoma. The patient was followed up and was found to be symptom free. A repeat PSG was carried out, and it was found that the episodic abnormal leg movements had completely disappeared [Figure 2].{Figure 2}

On the basis of current diagnostic criteria, PLMD is diagnosed when the following are present: (1) periodic limb movements in sleep (PLMS) documented by PSG; (2) PLMS exceeding norms for age (≥5/h for children); (3) clinical sleep disturbance or daytime fatigue; and (4) the absence of another primary sleep disorder or reason for PLMS, including Restless leg syndrome (RLS) and Obstructive sleep apnea (OSA).[6] Our patient fulfills the PSG and clinical domains of the diagnostic criteria for PLMD. Insulinoma has been reported to be associated with many types of movement disorders such as choreoathetosis, tremor, and dystonia.[7],[8],[9] But no literature associating hypoglycemia with PLMD is available. The possible hypothesis to explain the genesis of PLMD is probably the complex interactions between dopamine and insulin receptors in the hypothalamus. In animal studies, posterior hypothalamus has been found to have a relatively high concentration of insulin receptors.[10] Given the proximity of these receptors, it is possible that increased insulin level may cause reduction of nocturnal dopaminergic inhibition in this patient and lead to clinical presentation of PLMD. Literature search reveals that other movement disorders such as hypersomnia, night terrors, and rapid eye movement sleep behavior disorder have been described in association with insulinoma.[5],[11],[12]

Our case highlights the need for neurologists to keep in mind that hypoglycemia can also be a rare cause of PLMD, and all efforts should be made to rule out this reversible disease. If such episodes are missed, then it may lead to potentially devastating consequences.

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Conflicts of interest

There are no conflicts of interest.

All human and animal studies have been approved by the appropriate ethics committee and have, therefore, been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

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