Title : Pediatric case of benign monomelic amyotrophy involving the lower limb
Abstract:
Hirayama Disease, also known as Monomelic Amyotrophy (MMA), is a lower motor neuron disease that typically presents with an insidious onset of muscle weakness and atrophy most commonly in the upper limbs including the thenar, hypothenar, and forearm muscles.9 Neurologic sensation is usually intact and weakness plateaus after 2-5 years. The term “monomelic” refers to the observation that this disease usually affects a single limb, while amyotrophy refers to the wasting of muscle tissue. This disease was first described in 1959 by Hirayama and only about 1500 cases have been described since primarily in Japan and India.15 While the classic presentation of this disease is isolated to the upper limb, a minority of cases affecting the lower limb have been reported in the last three decades. Described here is one such case.3-5
Patient is a 13 year-old male who presents with left quadricep muscle atrophy. A discrepancy between his left and right thigh muscles became apparent by age 8. Prior to this, he had been participating in school athletics without issue but has since refrained from sports. He is able to maintain activities of daily living by favoring his right side. Patient and collateral deny a history of trauma, vitamin deficiency, or familial bone, muscle, or nerve disease. Additional past medical history includes attention deficit disorder with hyperactivity treated with atomoxetine since the age of 10.
This patient’s adequate nutrition, unremarkable X-rays, and clinical history rules out, vitamin deficiencies, trauma, structural bone disorders (SCFE,LCP), and bone tumors as causes of his presentation. Additionally, his age, lack of disease progression, and focal presentation also rules out any inflammatory, or inherited myopathy. Thus, after excluding more common diseases, Hirayama disease, or Monomelic Amyotrophy, arises as a forerunner as this patient’s diagnosis.
Audience Take Away Notes:
- The purpose of this report is to draw clinical attention to a rare cause of asymmetric limb atrophy.
- It will be helpful to primary care clinicians in terms of quick recognition and referral to a neurologist.
