Rare case of Slimmer's Palsy Following Intermittent Fasting Diet

Neurologists in Malaysia recently reported a rare case of acute bilateral foot drop in a late adolescent female following a rapid weight loss attributable to intermittent fasting diet.

Isolated common peroneal neuropathy (CPN) is the most common lower extremity mononeuropathy and the third most common mononeuropathy overall in adults. It often associated with multiple aetiologies, such as trauma, hereditary neuropathies and iatrogenic causes.

Its relatively superficial anatomical course renders CPN to be susceptible to mechanical-related injuries and metabolic disturbances. Acute CPN that develops following rapid and excessive weight loss is rare and scarcely reported. Partly due to social media influence to be physically aesthetic, weight reduction diets have been gaining popularity in recent time. Association of weight reduction diet-like intermittent fasting and bilateral CPN is exceptionally rare.

Baharin et al report a case of 19-year-old female who presented with worsening bilateral foot drop following a rapid intentional weight loss by intermittent fasting diet. She lost 20% of her baseline body weight within a period of 4 months. Systemic disease and metabolic screenings for neuropathy differentials were unremarkable. Electrophysiological studies revealed severe entrapment neuropathy involving bilateral common peroneal nerves (CPN). Her confounding risk factors for CPN injury included contact sport activities and habitual leg crossing during sitting. Following a dietary modification and physical therapy she achieved complete recovery of weakness and function on follow-up.

Isolated bilateral CPN following rapid weight loss is relatively rare with up to 20% can be associated with extreme dieting. The most likely explanation is that extreme dieting in general promotes calorie deficits that eventually triggers significant loss of subcutaneous tissue, leading to conduction block consistent with entrapment neuropathy at the level of fibula head.

Duration of weight reduction diet and the rate of weight loss has been associated with the development of PN. A weight loss that exceeds five kilogram per month and persists for several months following has been the strongest risk factor for the development of CPN. Entrapment neuropathy in this lady was exacerbated by her habitual leg-crossing tendency and her contact sport activities. After reverting to normal balanced diet and avoidance of further insults, she regained complete recovery of her bilateral foot weakness within 3 months.

Given the growing popularity of weight reducing diets in recent time, physicians have to anticipate this rare but reversible neurological disorder, which will increase in prevalence in the near future. The clinicians must be aware of pathophysiologic processes underlying this condition and its favourable outcome if recognized earlier.

Reference : Baharin, J., Yusof Khan, A.H.K., Abdul Rashid, A.M. et al. Slimmer's palsy following an intermittent fasting diet. Egypt J Neurol Psychiatry Neurosurg 58, 157 (2022). DOI: https://doi.org/10.1186/s41983-022-00594-3