Answer to Medical Challenge | Muscle Weakness

Posted on August 29, 2011

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The correct answer is E) Dermatomyositis.  This patient presents with proximal muscle weakness and a characteristic rash (Gottron’s papules) over the extensor surfaces commonly seen with this condition.  The most common etiology proposed is autoimmune (on muscle biopsy, CD4+ T-cells can be found associated with blood vessels), but dermatomyositis is associated with increased risk of malignancy, and in some cases has been presented as a paraneoplastic condition.  Other characteristic findings include Gottron’s papules, “heliotrope” rash, increased creatine kinase, and EMG changes consistent with a myopathy.

Explanations:

Myasthenia gravis (A) is incorrect because patients will describe a characteristic “fatigability” and a progression of weakness as the day goes on or with prolonged activity.  This is a disease of the neuromuscular junction, where autoantibodies prevent acetylcholine from activating its receptors on the surface of muscle fibers.  Diplopia (double vision) and ptosis (sagging eyelid) are also common complaints.  MG is associated with thymoma, and prophylactic thymectomy is often part of treatment.

Peripheral neuropathy (B) is incorrect because one would expect sensory deficits and/or decreased reflexes to accompany weakness.  Vibratory and temperature sensation are commonly lost well before weakness occurs, and especially in the distal extremities (the longest nerves are affected first).

Though there is a lung mass that cannot be identified by examining the radiograph alone, this patient’s presentation is not consistent with pneumonia (C).   A patient with a heavy smoking history who presents with vague symptoms and complains of cough will undoubtedly receive a chest x-ray, and while most are negative, this patient’s was revealing.

As opposed to the perivascular inflammatory response in dermatomyositis, polymyositis (D) displays a perifascicular (around the muscle cells) infiltrate of CD8+ T-cells; like dermatomyositis, creatine kinase is elevated.  Additionally, polymyositis is not associated with increased risk of malignancy.

Spinal cord compression (F) would also likely cause reflex anomalies, and if it were high enough to cause upper extremity weakness, one may expect to find UMN (upper motor neuron) signs in the lower extremities, and potentially autonomic dysfunction like incontinence of bowel or bladder.

While Creutzfeldt-Jakob disease (G) may cause motor anomalies (most notably, myoclonus), this patient’s history is not suspicious for CJD.  Patients with CJD will often present with a rapidly-progressive dementia that along with myoclonus and EEG changes clinches the diagnosis.

Finally, Guillain-Barré syndrome (H) is characterized by an ascending paralysis that begins with the distal musculature.  It often follows an upper respiratory tract infection or gastroenteritis (CMV, EBV, Mycoplasma, and Campylobacter are commonly-blamed agents).  CSF analysis often reveals albumino-cytologic dissociation (increased protein without an increase in white blood cells [pleocytosis]).

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Posted in: Medicine