Painless foot drop: an unusual acute presentation of new onset type 1 diabetes mellitus

Summary A 26-year-old Caucasian female with no past medical history or family history of auto-immune disease presented to the emergency department with new onset painless left foot drop. A panel of blood tests revealed blood glucose of 49.9 mmol/L and raised blood ketone levels. The patient was referred to the diabetes team who made a clinical diagnosis of type 1 diabetes (T1DM) and insulin treatment was initiated. Elevated levels of diabetes auto-antibodies were subsequently detected. Nerve conduction studies demonstrated a left common peroneal nerve lesion with conduction block at the fibular head. After 2 weeks of insulin treatment, a significant improvement of her foot drop was observed and after 8 weeks she was walking normally. The most probable cause of her foot drop was acute diabetic mononeuropathy. To our knowledge, there are no similar cases in adult patients reported in the literature. Our case highlights the importance of physicians being aware of atypical presentation of new onset T1DM. Learning points There is an increasing incidence of T1DM with more than half of patients presenting after the age of 20. Diabetic peripheral neuropathy can present both acutely and as a mononeuropathy. Although rare, clinicians should be aware of mononeuropathy as a presenting symptom of T1DM to avoid delay in the treatment initiation. This case highlights an unusual presentation of T1DM and illustrates the importance of the early diagnosis and management of T1DM.