A case of proximal muscle weakness and areflexia with post exercise facilitation of deep tendon reflexes

Abstract

Lambert-Eaton syndrome (LES) is a rare presynaptic neuromuscular junction disorder which is characterised by proximal limb muscle weakness, decreased deep tendon reflexes and various autonomic symptoms. A 60 year old gentleman presented with complaints of progressive proximal muscle weakness of both upper limbs and lower limbs since 6 months. He had significant weight loss and anorexia. He gave history of dryness of mouth, difficulty in swallowing and erectile dysfunction since past six months. On examination there was symmetrical, proximal more than distal, lower limb more than upper limb weakness. No wasting or fasciculation was noted. Gait was waddling. All deep tendon reflexes were absent. However, the reflexes showed a post exercise facilitation (after 10 s of tonic contraction) especially the knee jerk (video available). High frequency RNS performed showed an incremental response. Chest X ray showed a non-homogenous opacity in right middle zone. CECT thorax showed a heterogeneously enhancing lesion in right hilum involving mediastinum. A guided biopsy from lesion showed features of small cell neuroendocrine carcinoma. Anti-VGCC antibody was tested and it was positive confirming diagnosis of LES. Patient was transferred to oncology department and initiated on chemotherapy. I have obtained patient and Institutional Review Board approval. In conclusion, post exercise facilitation of deep tendon reflexes can be considered as the telltale sign of LES. LES is considered a harbinger of malignancy, especially small cell lung cancer (SCLC). A diagnosis of LES may lead to the timely detection of SCLC, significantly improving patient prognosis and survival.