Basic Human Neuroanatomy
A Clinically Oriented Atlas 
Case 77 Answers
1. Does this patient's weakness suggest an upper motor neuron or lower motor neuron process?

Lower motor neuron (LMN) process (weakness with atrophy and hyporeflexia).

2. Is there evidence of spinal cord involvement in this case and, if so, at what level?


3. Is there evidence of dorsal or ventral root involvement or spinal nerve involvement in this case, and, if so, what is the level(s) of the involvement?

No. The patient’s motor and sensory signs and symptoms do not follow a specific dermatomal or myotomal pattern.

4. Is there evidence of plexus or peripheral nerve involvement in this case? If so, indicate the specific structure(s) involved by the pathologic process.

Yes. The patient’s signs and symptoms suggest involvement of a specific peripheral nerve of the right sacral plexus, the tibial nerve, while sparing other nerves of the plexus (e.g., the common fibular (peroneal) nerve and more proximal nerves of the plexus). Numbness, tingling, and burning (hyperpathic) pain involving the plantar aspect of the right foot and toes, with variable, inconsistent spread up the posterior, distal aspect of the calf, plus the weakness of ankle plantar flexion, inversion of the foot, and flexion of the toes, suggest a lesion of the right tibial nerve.

5. Where is the anatomical location of the pathologic process leading to this patient’s condition?

Her right tibial mononeuropathy appears to be localized to the middle of the popliteal fossa above its branches to the gastrocnemius and soleus muscles, since those muscles, as well as the muscles of the deep posterior compartment of the leg, are involved by the pathologic process.

6. In general, what type of pathological process do you think is involved in this case?

The most likely pathological process in this setting is a compression or pressure neuropathy; although the specific mechanism of compression is not clear from the patient’s history. However, as mentioned in other similar cases, mononeuropathies can also be caused by amyloid or tumor infiltration and ischemic, infectious, or inflammatory processes such as diabetes, leprosy, sarcoidosis, vasculitis, and autoimmune diseases.

7. What diagnostic procedure(s) would you undertake at this point? 

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