Compassionate use of orphan drug 3,4-Diaminopyridine(DAP) in Treatment of Lambert Eaton Myasthenic Syndrome (LEMS). 3,4-DAP is used to decrease the muscle weakness associated with LEMS and hopefully will decrease the need for prednisone and all other therapies that were previously required to control symptoms. How long a patient will take 3,4 DAP depends upon if he/she is seeing benefits from the medication or experiencing side effects that will prevent them from continuation in the study.

3,4-diaminopyridine (3,4-DAP) decreases symptoms of weakness in patients with LEMS, and therefore can be used to decrease the amount of immune modulation therapy needed to provide an equivalent degree of disease control.

Inclusion Criteria:

1. Clinical diagnosis of LEMS with or without any of the following: evidence of underlying malignancy, presence of P/Q or N-type calcium channel antibodies, electrodiagnostic evidence of a presynaptic defect of neuromuscular junction transmission.None of these laboratory findings are required for inclusion in this study.
2. P/Q and N type calcium channel antibodies are measured in the blood as a routine laboratory test during the course of initial diagnosis, but 10-20% of patients with LEMS do not have elevated levels of these antibodies.

Exclusion Criteria:

1. Hypersensitivity to any component of this medication.
2. History of past or current seizures.
3. History of asthma.
4. Evidence of prolonged QT syndrome. There is no absolute upper limit of normal for the QTc interval.
5. Family history of prolonged QTc syndrome, history of unexplained syncope, seizures or cardiac arrest.