SMA involves atrophy of skeletal muscles. Werdnig-Hoffmann disease is synonymous with SMA type I, which involves severe, early onset (first few months of birth) SMA. Dubowitz disease is synonymous with SMA type II (intermediate), which involves onset at around 6-18 months age. Kugelberg-Welander disease, also known as juvenile SMA, is synonymous with SMA type III, and involves the affected individual being able to walk without support at some time, but the probable loss of this ability later in life. SMA type IV does not have an associated eponym, and there is no SMA type V.

The obturator nerve innervates skin of the medial aspect of the thigh. It is also responsible for the motor innervation of the adductor muscles of lower extremity (external adductor longus, adductor brevis, adductor magnus, and gracillis). The obturator nerve is derived from spinal nerves L2-L4. Damage to the obturator nerve would result in weakness in adduction and lateral swinging of the leg due to unopposed abductors.

Meningitis is an illness that features fevers, headaches, and stiff necks. This is a serious illness that can be fatal if not treated promptly. It typically begins showing symptoms 3-7 days after exposure. If the infection is bacterial in origin, it can be treated effectively with antibiotics. If it is viral, the treatment is supportive in nature.

You would expect this patient to exhibit wrist drop.

This is a multi-step thinking question that gives you many clues as to what might be wrong in the patient. First, let's sort out the facts that we are given:

1. The patient has a break in the middle of his right humerus.

2. Patient has numbness on the dorsal surface of his ipsilateral (same side) hand.

3. Patient is unable to extend (straighten) his elbow.

Now let's ask ourselves some questions about these facts:

1. What is the anatomy of the humerus, specifically in the mid-shaft? (hint: what "groove" is located there?)

2. What nerve provides sensation to the dorsum of the hand?

3. What muscles extend the elbow and what nerve innervates those muscles?

The spiral groove is located in the middle of the humerus, which is where the radial nerve wraps around the bone. The radial nerve supplies sensation to the dorsum of the hand. The triceps brachii are responsible for straightening the elbow and are innervated by the radial nerve. Fomr the given information, we know the radial nerve is likely injured, but we need to figure out what else could be impacted by this deficit. The radial nerve innervates the extensor muscles of the forearm, allowing one to extend at the wrist. If these muscles were to be deficient, as exhibited in a radial nerve injury, one would expect the wrist to not be able to extend, and thus manifest as wrist drop.

Let's touch on the other answer choices for further learning:

Claw hand is seen in ulnar nerve injury such as Klumpke's paralysis and manifests as a weakness/inability to flex the wrist (flexor carpi ulnaris), the metacarpophalagneal joints of the 4th and 5th digits in extension (interosseous muscles), and interphalagneal joints of the 4th and 5th digits in flexion (also interossei and lumbricals).

Erb-Duchenne Palsy or Erb's Palsy is an injury to the upper trunk of the brachial plexus that occurs when the head is violently displaced from the shoulder as happens in a difficult breech delivery or trauma. This will involve the suprascapular, musculocutaneous, and often axillary nerves. Patients present with the arm adducted (deltoid muscle deficient), elbow extended (biceps brachii deficient), and forearm pronated (also biceps brachii). This is referred to as the "waiter's tip" position.

Carpal tunnel syndrome is entrapment of the median nerve in the carpal tunnel (beneath the transverse carpal ligament). Patients present with numbness and tingling in the palm of the hand as well as 1st, 2nd, 3rd, and half of the 4th digits. There may be atrophy of the thenar eminence, as well as weakness in thumb opposition. Symptoms are worse at night.

Anterior interosseous nerve (AIN) syndrome is a rare median nerve entrapment that will manifest similar to carpal tunnel syndrome, but is distinguished by its presentation of only motor symptoms and lack of nighttime symptoms.

Autism Spectrum Disorder (ASD) has a wide range of signs or symptoms. These can vary from mild to severe, depending on the individual. There is no single cause for autism and there is no cure. Treatment includes management of behaviors, therapy, interventional services.

The sciatic nerve is a large nerve that runs through the buttocks and down the lower limb. The sciatic nerve innervates skin of the leg, and muscles in the posterior thigh, leg, and foot. The sciatic nerve is derived from spinal nerves L4-S3. Damage to the sciatic nerve would result in impaired hip extension and knee flexion. It would also lead to a loss of plantar/dorsiflexion and inversion and eversion of the foot.

The deep fibular nerve is also known as the deep peroneal nerve. The deep fibular nerve supplies branches to the tibialis anterior, extensor digitorum longus, peroneus tertius, and extensor hallicus longus. The common fibular nerve is derived from spinal nerves L2-L4 and branches off to the superficial and deep fibular nerves. Damage to the fibular nerve is often caused by traumatic injury to the lateral knee; this results in a foot drop which causes the affected person to walk with a high stepping gait.

Drop foot is observed as an unusual gait, where the foot drops due to weakness in the tibialis anterior, and associated dorsiflexors, or to damage to the deep fibular nerve. The deep fibular nerve innervates the anterior compartment of the lower leg, where the dorsiflexors originate. Injury to this nerve would make a person unable to dorsiflex her ankle, causing it to drag/present as a drop foot.

Tarsal tunnel syndrome occurs when the tibial nerve is compressed against the flexor retinaculum of the foot and or portions of the talus and calcaneus, as these three structures comprise the tarsal tunnel. Typically, patients with tarsal tunnel syndrome will report numbness, pain, and/or a tingling sensation radiating to the hallux.

The axillary nerve, which originates from the C5 and C6 spinal roots, provides motor innervation to the deltoid and teres minor muscles, both abductors of the shoulder. It also provides sensory input to the lower deltoid via the superior lateral cutaneous nerve. Damage to this nerve is a possible complication during an axillary dissection. If a patient had sustained an injury to this area they would have difficulty abducting or raising the arm laterally.