Left arm brachial neuritis 1 month post 2nd COVID19 vaccine dose, verified by neurology consultation (neuromuscular) at the Medical Center including electromyography / nerve conduction studies. Pfizer Dose #1 was administered on 02/10/2021 at 2:30PM by intramuscular injection in the left deltoid region; Pfizer Dose #2 was administered on 03/05/2021 at 7:40AM by intramuscular injection in the left deltoid region. Severe left shoulder and arm pain began 04/05/2021, followed within 36 hours by fasciculations and weakness. Moderate pain lasted 6 weeks, despite high-dose analgesics/anti-neuropathic pain medications. There is mild, permanent weakness. See Continuation Page for additional clinical details.  The first COVID-19 vaccine dose administration (February 10, 2021 [2:30PM], left deltoid intramuscular injection, Hospital) was fully uncomplicated without any notable symptoms. The second COVID-19 vaccine dose administration (March 5, 2021 [7:40AM], left deltoid intramuscular injection, Hospital) was uncomplicated at the time of administration, but there was progressive left deltoid soreness starting 8 hours after the dose, followed by headaches starting 10 hours after the dose. The next 24 hours were marked by deltoid soreness, headaches, and general malaise, but all symptoms resolved within about 36 hours after the dose.  On 4/5/21 (1 month post COVID-19 vaccine dose #2), I awoke with a dull but fairly severe aching pain centered around my left shoulder and triceps region, with some extension to my forearm and scapular regions that waxed and waned a bit. Qualitatively it almost felt "ischemic" (in the sense of a tourniquet sort of ache rather than "neuropathic" in the sense of burning or electrical), and I rated it about a 5-6/10 in severity and it made it very hard to concentrate on anything else. There was no antecedent injury. Initially, there was no weakness, adventitious movements, sensory change, or vascular change in the limb. There seemed to be some muscle tenderness and spasm around the supraspinatus and, to a lesser extent, rhomboids. However, massaging it didn't help much or even really seem to relate to the main pain in terms of quality and location. There was no pain-free position for the limb, but the severity of the pain was position-related --- the most comfortable position was lying down with my left hand behind my head and elbow pointing up towards the ceiling. And just letting my arm hang passively while standing was excruciating. The most painful maneuvers seemed to involve leaning forward and allowing my shoulder blades to move superiorly (as in reaching to pick something off the floor or leaning forward to wash my hands at the sink --- in retrospect, these were movements that put stretch on the brachial plexus). I could prevent increases in the pain during these otherwise provocative maneuvers by deliberately activating my back muscles to keep my scapulae pinned more inferiorly.   Within 36 hours, the pain intensified, and fasciculations in the muscles of the left upper extremity and shoulder girdle/torso began. The most obvious initially was the triceps --- there were rhythmic runs of twitching in what felt perhaps like muscle fibers or fascicles deep in the muscle belly. Others were present in the wrist extensors, as well as occasionally in the pectoralis muscles and the torso on the left. Weakness was greatest in the triceps from early on. Prior to the onset of the illness, I would routinely do at least 9 plank push-ups in a set. After the onset 4/5/21, I was able to hold a plank position, but I was unable to complete a single push-up. On attempting a push-up, my left triceps buckled immediately and I collapsed to the floor as soon as I started to flex at the elbow as part of the descent phase of the push-up. Lesser amounts of weakness were present in multiple muscles around the left shoulder girdle.  On 5/3/21 (4 weeks post onset of symptoms), electromyography withe nerve conduction studies corroborated the suspected clinical diagnosis of brachial neuritis. "INTERPRETATION: This study shows mild acute denervation changes in several brachial plexus muscles affecting primarily the upper trunk."  In total, the pain lasted for 6 weeks, despite continuous anti-neuropathic, anti-inflammatory, and analgesic medications; I declined steroid treatments due to concern over side effects. For the first week, the pain was excruciating (rarely less than 5-6/10, with frequent spikes up to 8-9/10) with the epicenter of pain mostly deep within the shoulder area. Around day #8 or 9, there was a gradual transition to more moderate pain (mostly 3-5/10 that occasionally waxed to 5-7/10 with rare "spikes") with the epicenter of the pain more around the elbow than the shoulder. There was still moderate pain at one month, and only in the final 1-2 weeks did the pain gradually wane. This was all through gabapentin 2400mg/day; NSAIDS (either 880mg/day naproxen or 2400mg/day ibuprofen); and 2250mg/day acetaminophen. When I missed a dose, things became worse for several hours (~7/10), and I had difficulty getting the pain under control easily, even after taking subsequent medication doses.  Recovery from weakness has been substantial, but there is still mild, residual triceps and shoulder girdle weakness at 9 months after onset that is likely permanent.