Deep Tendon Reflexes in Myopathy
Deep tendon reflexes are typically preserved or normal in most myopathies, which is a key distinguishing feature from neuropathies where reflexes are characteristically reduced or absent.
Clinical Pattern
In myopathic conditions, the reflex arc remains intact because the pathology affects the muscle fibers themselves rather than the peripheral nerves or neuromuscular junction. This preservation of reflexes helps differentiate myopathies from neuropathies during clinical examination 1.
Key Examination Findings
- Reflexes: Usually normal or preserved, even in the presence of significant muscle weakness
- Sensory examination: Normal (no sensory deficits)
- Sensory nerve conduction studies: Normal responses
- Pattern of weakness: Typically proximal and symmetric
Important Exceptions and Caveats
When Reflexes May Be Reduced or Absent in Myopathy
Specific myopathy subtypes can present with reduced or absent reflexes, creating diagnostic confusion:
Myotonic dystrophy: Tendon reflexes are frequently absent or weak despite being a primary muscle disease 2. This occurs due to selective atrophy of Type 1 muscle fibers, which are preferentially involved in deep reflex responses.
Congenital myopathies: Particularly those with Type 1 fiber predominance or atrophy (such as centronuclear myopathy and congenital fiber type disproportion) may show areflexia 3. The mechanism involves dysfunction of muscle spindles or impairment of the fusimotor system.
X-linked myotubular myopathy carriers: Manifesting carriers frequently demonstrate reduced or absent deep tendon reflexes (45% in one cohort) 4.
Critical illness myopathy: Patients may develop absent deep-tendon reflexes in the setting of sepsis and multiple-organ dysfunction 5.
Clinical Algorithm for Distal Weakness
When evaluating a patient with distal weakness 1:
- Preserved reflexes + no sensory deficit → Favors myopathic cause
- Absent reflexes + sensory changes → Favors neuropathic cause
- Confirm with EMG: Myopathic changes (short duration, low amplitude polyphasic potentials) versus neuropathic changes
Practical Diagnostic Approach
For inflammatory myopathies (polymyositis, dermatomyositis), reflexes remain normal unless there is severe muscle atrophy or coexisting neuropathy 6. The diagnostic workup should include:
- EMG showing myopathic pattern (polyphasic motor unit action potentials of short duration and low amplitude)
- Muscle biopsy for definitive diagnosis
- Elevated muscle enzymes (CK, aldolase)
Common pitfall: Don't assume areflexia automatically excludes myopathy—consider myotonic dystrophy and congenital myopathies in the differential when reflexes are absent with a myopathic presentation.