Spasticity

Muscle Selection, Dosing Administration

Muscle selection
A working knowledge of primary clinical patterns of muscle spasticity is essential to individualizing BTX-A therapy. BTX-A injections are most effective in relieving focal spasticity around a joint or series of joints. Even though BTX-A is a focal treatment, untreated muscles may benefit from the disruption of the synergy patterns that often replace isolated muscle control. Clinicians should realize that adjacent muscles usually have some reduction in tone. Controlled tone reduction through BTX-A injections must not interfere with existing patient function. For example, in a non-ambulatory patient, complete weakness of the thigh adductors or gastrocsoleus may be appropriate, whereas in the ambulatory patient, only mild tone reduction may be sufficient. Since it is not always practical to treat all muscles in one visit, the treatment team should prioritize muscles to be injected. Synergic muscles or sites remote from the original injections may need to wait for follow-up treatment. Also, additional problematic muscles may be exposed by previous BTX-A injections, requiring subsequent BTX-A treatment as well.

Outcomes should be evaluated by a range of clinical measures, including rating scales and video tape recordings, that reflect clearly defined goals and objectives. Focal clinical patterns that may benefit from BTX-A treatment include:

Upper Limb Adducted/internally rotated shoulder Flexed elbow Pronated forearm Flexed wrist Thumb-in-palm Clenched fist Intrinsic plus hand

Lower Limb Flexed hip Flexed knee Adducted thighs Stiff (extended) knee Equinovarus foot Striatal toe (Hitchhiker's great toe)

 

The Adducted/Internally Rotated Shoulder: This patient with head injury demonstrates an adducted/internally rotated shoulder, flexed elbow, pronated forearm, bent wrist, and clenched fist. The patient also has a thumb-in-palm deformity. See Muscles.	The Flexed Elbow: This patient would often drive his fist into his throat because of severe elbow flexor spasticity. See Muscles.
The Pronated Forearm: Pronator quadratus and/or pronator teres may contribute to the pronated forearm deformity. See Muscles.	The Flexed Wrist: Severe spastic wrist flexion may sometimes lead to wrist subluxation and carpal tunnel syndrome. See Muscles.
The Clinched Fist: Two years after head injury, this patient illustrates a clenched fist with likely involvement of flexor digitorum sublimis. Flexor pollicis longus contributes to the thumb-in-palm deformity. See Muscles.	The Thumb-in-Palm Deformity: Eleven months after head injury, this patient illustrates thumb-in-palm deformity when he tries to open his hand. Dynamic EMG studies reveal that flexor pollicis longus, adductor pollicis, and the thenar muscles all contributed. A parallelogram type of finger electrogoniometer records motion across the third finger PIP joint. See Muscles.
Equinovarus: Varus posture may be seen in this patient from the anterior view. Excessive pressure typically occurs under the fifth metatarsal head. See Muscles.	Striatal Toe: Striatal toe (hitchhiker's great toe) caused by an overactive extensor hallucis longus. See Muscles.
Stiff Knee: Persistent knee extension of the "stiff knee," shown here with marked equinus. Note that the heel is not in contact with the foot pedal of the wheelchair. See Muscles.	Flexed Knee: Flexed knee deformity. Note taut hamstring tendons. See Muscles.
Adducted Thighs: The "scissoring thighs" caused by spastic adductors produce a narrow base of support at the feet. See Muscles.

Dosing
A consensus on initial doses and dose ranges by muscles for pediatric and adult patients has been established by the Spasticity Study Group, a committee of clinicians who are experts in the use of BTX-A to treat spasticity. Several dose-modifiers must be considered in making possible adjustments in the amount of BTX-A used within the given muscle range. Patients with a clinical profile that suggests a lower initial dose may begin with injections at the low end of the range and those with a higher dose profile may start at the high end. The dose used for those patients who fall in between is left to the discretion of the experienced clinician. Given the number of variables involved, clinical experience is an important factor.

Administration
The number of injection sites is primarily determined by the size of the muscle. Theoretically, it may be appropriate to inject more sites with smaller doses. More injection sites facilitate a wider distribution of BTX-A to nerve terminals. Too many injection sites, however, may contribute to the undesirable use of BTX-A on areas, such as the musculotendinous junction, where no nerve terminals exist. One should consider decreasing the number of injection sites or certain pediatric patients to minimize discomfort.

The proper targeting of muscles is a crucial factor in achieving efficacy and reducing adverse effects from BTX-A injections. Proficiency in dosing and injecting BTX-A demands skill development. Difficult-to-localize muscles often require adjunctive imaging methods (EMG, ES, CT, fluoroscopy, and ultrasound) to confirm injection sites. The objective in EMG or ES monitoring is to target the region of maximum muscle activity.