Left Thigh Muscle Shrinking, Reduced Motor Power, Cramps And Lost The Patella Reflex In The Left Leg. Suggestions?

Age: 42 years
Sex: Male
Left thigh muscle shrinking, reduced motor power, cramps and lost the patella reflex in the left leg
History:
The first symptoms showed up 2010.
Thigh muscle in left leg was twitching but wasn't painful. The twitching of the thigh muscle was in and out but did not affect walking or mobility.

Approx. a year later, I noticed changing in the size of the thigh muscle (shrinking) also the twitching was accompanied by cramps in the muscle and sensation of numbness in the knee area and thigh muscle area.
Checked with my doctor. Patellae reflex wasn't that good in my left leg (was delayed by 1-2 seconds after testing).
Lab findings:
Anti-MuSK antibody 01 Antinuclear antibodies (ANAs) 01
Albumin:57.8 a1 globuline: 2 a2 globuline:9.6 b globuline: 12.6
gamma:17.9 CPK:150 U/I ASLO (Quantitative)
C-reactive protein
2011: X Ray for backbone (Did not show anything)
Patella reflex by this time was absent.

June 2012: Interference EMG (Left, Vastus lateralis, Femoralis, L2-L4)
MUP amplitude:increased, MUP duration: increased,
MUP polyphasicity:increased, Pattern: Neurogen

Meanwhile my left thigh has been shrinking being quite visible and reducing the size by 4 cm in circumference .Of course the power in my left leg diminished quite a bit, but still being able to walk without no problem but some task were difficult to manage like walking up steep ladder steps or executing squats was quite challenging and had to rely mostly on the right leg.
2013: Ultrasound (abdominal section): Nothing peculiar has been noticed.
2013: MRI for backbone and skull: Did not show any thing conclusive.

2013 (Sept) result: MRI of the Pelvis/Lumbosacral Plexus/Left Inguinal Region

History: Right femoral neuropathy.
Technique: Lumbosacral plexus: Axial Tl, axial FSE T2, axial and coronal STIR. Inguinal region: Axial Tl, axial FSE T2 with fat-sat, sagittal STIR
Findings:
The study of the lumbosacral plexus demonstrates no evidence of a presacral or retroperitoneal mass. In particular, the region of the sacral ala is normal bilaterally. Though the study was not tailored to lumbosacral spine, no disc herniations, central canal stenosis, or bony neural foraminal stenosis is seen. The sacroiliac joints are well-maintained. The piriformis muscle demonstrates slight asymmetry, with slightly increased bulk of the right piriformis, but of course clinical correlation is required. The regional bone marrow signal is maintained. Incidental note is made of a partially imaged 4.3 cm high T2 signal lesion of the right kidney, which contains a septum, and ultrasound is recommended for complete assessment. The visualized abdominal aorta is of normal caliber.
The study of the bilateral inguinal region extends from the inguinal region to the adductor canal and demonstrates there to be no evidence of an inguinal hernia, or of significant lymphadenopathy. The region of the course of the femoral nerve is unremarkable. The regional muscles and tendons demonstrate a normal signal, and both the joints are well maintained. The regional bone marrow signal is again normal.
Impression:
1. No etiology for lumbosacral plexopathy is demonstrated.
2. The left inguinal region, and course of the left femoral nerve are also unremarkable.