Weak; cramps in her legs when she sleeps; Unsteady; gets worn out real fast; This is a spontaneous report from a contactable consumer (patient) based on information received by Pfizer.  On 13Nov2020, a spontaneous report was received from a consumer regarding a 70-year-old female who was being treated with FIRDAPSE 10 MG (amifampridine). On 19Jul2021, additional information was received from a consumer, and based on the information received, the case was upgraded to serious/unexpected and COVID vaccine was added as a co-suspect. Medical history included generic myasthenia syndrome, COPD (chronic obstructive pulmonary disease), arthritis with joint pain "as she gets older," depression, irritable bowel syndrome, osteopenia, problems with her stomach, and prior use of dicyclomine 10 mg for problems with her stomach (gastric disorder)/irritable bowel syndrome (she stopped taking on an unspecified date because it didn't seem to be helping). Concomitant products included: citalopram 20 mg once daily for depression, omeprazole 40 mg once daily, losartan 100 mg once daily, Mestinon (pyridostigmine bromide) 60 mg at 90 mg 4x/day for genetic myasthenic syndrome, zinc 50 mg daily, albuterol as needed, Symbicort 4.5 ug 2x/day (started by her lung doctor on an unspecified date in Nov2020, "a week ago;" relative to 13Nov2020), and Prevacid (lansoprazole) one tablet daily. On 22Oct2020, the patient started treatment with FIRDAPSE 10 MG at 5 mg 3x/day orally for genetic myasthenic syndrome. On an unspecified date in 2020, the dose was increased to 10 mg 1x/day and 5 mg 2x/day for 4 days. Followed by a dose increase to 10 mg 3x/day (2020). On an unspecified date in 2020, after starting the product and within 30 minutes to an hour after each FIRDAPSE dose, the patient experienced numbness and coldness in her feet and especially her hands, tingling lips, and a runny nose. The events would last for "maybe 15 to 30 minutes" before resolving and would return following the next FIDAPSE dose. No action was taken with the product as a result of the events. As of 13Nov2020, treatment with FIRDAPSE was ongoing as were the events of numbness and coldness in her feet and hands, tingling lips, and runny nose. No additional information was provided. On 19Jul2021, the patient's medical history was updated to include congenital myasthenic syndrome, LEMS (Lambert-Eaton myasthenic syndrome), multiple allergies, acid reflux, high blood pressure, high cholesterol, and allergies to grass (seasonal allergy). Concomitant products were updated to include simvastatin and ibuprofen. On 21Oct2020 (previously reported as 22Oct2020) the patient started treatment with FIRDAPSE for congenital myasthenic syndrome/LEMS. Since day 1 of starting FIRDAPSE, the patient had experienced a cold feeling and tingling in her hands, fingers, nose, mouth, and lips. It would happen for about 15 minutes after taking the medication and then it was over. On an unspecified date in 2020, the patient's FIRDAPSE dose was increased to 15 mg in the morning, 15 mg in the afternoon, and 1 tablet (10 mg) in the evening. Around 07Mar2021, the patient went to the ER (emergency room) for COPD. She was having trouble breathing and her heart was beating fast at 115 bpm (beats per minute). On 26Apr2021, the patient received her COVID vaccine (unknown lot/batch number; unknown dose number, single). On an unspecified date in 2021 about 3 months ago (relative to 19Jul2021) (also reported as over the past month, relative to 19Jul2021), the patient had been feeling unsteady and weak. She had to use her cane and walker but got "worn out real fast" (2021). The patient had been doing more physical activity by getting her camper ready for camping season. She did not know if the increased physical activity, her COVID vaccine, or her allergies to grass contributed to her feeling unsteady and weak. On an unspecified date in Jun2021 (reported as about a month ago, relative to 19Jul2021), the patient had experienced cramps in her legs when she slept. She thought overuse of her muscles might have caused the cramps as they did not happen in the winter. As of 19Jul2021, treatment with FIRDAPSE and the statuses of cold feeling and tingling in her hands, fingers, nose, mouth, and lips were ongoing. The statuses of COPD, heart was beating fast, feeling unsteady, weak, got worn out real fast, and cramps in her legs were not reported. The patient had not sought medical advice or treatment for feeling unsteady and weak. No additional information was provided. The action taken in response to the events for amifampridine phosphate was unknown. The outcome of the events leg cramps, weakness, unsteady gait and fatigue were unknown while the outcome of the events was not recovered.  Comment: A 70-year-old female who started treatment with FIRDAPSE for congenital myasthenic syndrome/LEMS on 21Oct2021 experienced the following events after each dose: a cold feeling and tingling in her hands, fingers, nose, mouth, and lips. The events would last for 15 minutes. On an unspecified date, the patient's FIRDAPSE dose was increased. Around 07Mar2021, she was evaluated in the ER due to COPD. She was having trouble breathing and her heart was beating fast at 115 bpm (beats per minute). No further details were provided. Since then, she has received her COVID vaccine, has been feeling unsteady and weak, and had leg cramps while sleeping. As of last report, cold feeling and tingling in her hands, fingers, nose, mouth, and lips were ongoing and are likely related. COPD flare is unlikely related and due to exacerbation of underlying disease. Tachycardia is likely due to COPD flare Unsteadiness, weakness, and leg cramps are likely due to LEMS.   The lot number for the vaccine, [BNT162B2], was not provided and will be requested during follow up.