25 - Peripheral Nervous System and Skeletal Muscle

Guillain-Barre Syndrome (GBS)

A 30-year-old male patient presents with symmetric ascending paralysis and areflexia following a history of diarrhea. What is the most likely diagnosis?

Campylobacter jejuni, CMV, EBV, and Mycoplasma

Microbial infections associated with GBS

Albuminocytologic dissociation - ↑ CSF protein without significant ↑ in inflammatory cells

CSF finding in GBS

Chronic inflammatory demyelinating polyradiculoneuropathy

Most common chronic acquired inflammatory peripheral neuropathy

Diabetes Mellitus

Most common cause of peripheral neuropathy

Distal symmetric sensory polyneuropathy (Glove and stocking pattern)

Characteristic pattern of involvement in diabetic neuropathy

Sorbitol

Accumulating substance that causes osmotic damage in diabetic neuropathy

Charcot-Marie-Tooth disease

Most common inherited peripheral neuropathies

Antibodies to postsynaptic ACh receptor

Autoantibodies linked to myasthenia gravis (MG)

Thymic hyperplasia, thymoma

Thymic abnormalities associated with myasthenia gravis

↓ response with repeated stimulation

Electrophysiology finding in MG

Antibodies to presynaptic Ca channel

Autoantibodies linked to Lambert-Eaton myasthenic syndrome (LEMS)

Neuroendocrine lung carcinoma

Lung cancer associated with LEMS

↑ response with repeated stimulation

Electrophysiology finding in LEMS

Dermatomyositis

Most common inflammatory myopathy in children

Paraneoplastic disorder

Dermatomyositis in adults usually occur as a form

Perifascicular atrophy

Morphologic hallmark of dermatomyositis

Heliotrope rash

Lilac-colored rash on upper eyelids

Gottron papules

Dusky red patches on knuckles, elbows, and knees

Anti-Mi2

Autoantibodies associated with Gottron papules and heliotrope rash

Anti-Jo1

Autoantibodies associated with interstitial lung disease, Nonerosive arthritis, Skin rash ("mechanic's hands")

Polymyositis

Similar symmetric proximal muscle weakness involvement with dermatomyositis but absent cutaneous manifestations

Total absence of dystrophin (Deletion/Frameshift)

Genetic mutation in Duchenne muscular dystrophy (DMD)

Truncated version of dystrophin (↓ activity)

Genetic mutation in Becker muscular dystrophy

Creatine kinase

Enzyme elevated in early stages of DMD but decreased in the late stages

NF2 loss

Etiology of schwannoma

Vestibular schwannoma

Type of schwannoma located in the cerebellopontine angle, attached to vestibular branch of CN VIII

Antoni A

Cell-dense area of palisading spindle cell fascicles in schwannoma

Antoni B

Cell-poor areas with prominent myxoid stroma

Neurofibroma

Most common peripheral nerve sheath tumors

NF1 loss

Etiology of neurofibroma

(Neurofibromin, Ch17) loss → ↑ RAS signaling

Etiology of neurofibromatosis type 1

NF2 (Merlin, Ch22) loss

Etiology of neurofibromatosis type 2

Neurofibromatosis type 1

Malignant peripheral nerve sheath tumors, optic nerve gliomas, pheochromocytoma, Lisch nodules, Cafe au lait spots

Neurofibromatosis type 2

Schwannoma, meningioma, ependymoma