Classes of conditions determined by biopsy include congenital myopathy; muscular dystrophies; metabolic, vasculitis, glycogen storage diseases; mitochondrial myopathy; connective tissue disease; myositis; traumatic, infectious, and neurogenic changes.
Avoid recently traumatized muscle, including the puncture sites where needles were placed during electromyographic studies to avoid needle necrosis, and muscle distal to a known neuropathy or affected by another condition. Frequently utilized sites include the biceps, deltoid, vastus lateralis, and quadriceps. For inflammatory myopathies, a fascial sample may be helpful.
The neuropathology department should be on notice prior to starting the procedure for quick sample pick-up. The patient is placed in the supine position. One should then identify, drape, and prep the selected limb in the standard fashion. Lidocaine 0.5% is injected subcutaneously (without epinephrine), with care to not infiltrate the muscle. A skin incision of 2 cm is made with a scalpel over the biopsy site. Electrocautery should be avoided because it causes severe artifact. A self-retaining retractor is placed. The fascia overlying the muscle is then incised along its fibers (Fig. 102.1).
Fig. 102.1 Standard technique for muscle biopsy. Following skin incision and placement of small self-retaining retractor, the fascia is incised along its fibers. The muscle clamp is placed following the anatomic orientation of the muscle fibers, and a muscle sample is harvested sharply with scissors measuring at least 2 cm and 0.8 cm thick. 1. Muscle biopsy clamp; 2. resected muscle fiber; 3. fascia.
The belly of the muscle is identified, far from prior biopsy sites, and subfascial and myotendinous areas. Two discreet and intact muscle biopsy samples are extracted, with dimensions of at least 2 cm long and 0.8 cm thick (Fig. 102.1). The muscle fibers are cut sharply using scissors or a scalpel. The remainder of the surrounding muscle is injected with local anesthetic. Closure of the wound is achieved using 3.0 polyglycolic acid sutures (Vicryl ™, Ethicon, New Brunswick, NJ) for the skin and skin closure strips (Steri-Strips™, 3M Inc., St. Paul, MN). A dressing is applied to the wound.
This is an outpatient procedure. The patient may schedule a phone follow-up or may follow up in the clinic for suture removal. The patient should follow up with the referring physician to review the pathologic diagnosis and to discuss treatment planning.
5 O’Sullivan PJ, Gorman GM, Hardiman OM, et al. Sonographically guided percutaneous muscle biopsy in diagnosis of neuromuscular disease: a useful alternative to open surgical biopsy. J Ultrasound Med. 2006;25(1):1-6.
6 von Kempis J, Kalden P, Gutfleisch J, et al. Diagnosis of idiopathic myositis: value of 99mtechnetium pyrophosphate muscle scintigraphy and magnetic resonance imaging in targeted muscle biopsy. Rheumatol Int. 1998;17(5):207-213.