Related Subjects:
|Lung Cancer
|Hypercalcaemia
|Oncological emergencies
|Malignant Hyperparathyroidism due to PTHrP
|Lambert-Eaton syndrome (LEMS)
|Superior Vena Caval Obstruction syndrome
About
- Is classically seen as a paraneoplastic myopathy associated with small cell lung tumour s
- LEMS symptoms may precede the diagnosis of lung tumour .
- Can also be seen younger patients with autoimmune disease.
Aetiology
- LEMS results from an autoimmune attack against voltage-gated calcium channels (VGCC) on the presynaptic motor nerve terminal
- VGCC antibodies have been reported in 75-100% of patients with LEMS who have SCLC and in 50-90% of patients with LEMS without underlying cancer
- LEMS is associate with malignancy in only 50% of cases
Clinical
- Patients will complain of difficulty rising from a chair, climbing stairs, raising hands above head, early fatigue
- Notably affects proximal muscles less than oculobulbar (MG)
- Muscle strength and response improves with repetitive stimulation
- Respiratory weakness
- Autonomic symptoms - dry mouth, constipation, impotence, bladder dysfunction
Differential
- Myasthenia gravis
- Myopathy because of proximal weakness
- Motor neurone disease
Investigations
- Tensilon test negative
- Ab to P/Q type voltage-gated calcium channels (VGCC)
- Ab to M type voltage-gated calcium channels (VGCC)
- Electrodiagnostic tests - small polyphasic potentials, increased jitter
- CXR and Bronchoscopy and CT chest/PET scan to look for primary lung cancer
Management
- Steroids and Azathioprine not as useful as in MG
- Plasma exchange and IVIG may be useful
- 3,4-diaminopyridine which blocks potassium channels and prolongs action potential duration
Prognosis
- Surveillance annually for malignancy