Disclosures: Michael D. Warwick, MD: No financial relationships or conflicts of interest

Case Diagnosis: Myotonic Dystrophy, Type 1

Case Description: A 45-year-old male police officer with no significant medical history presented with one year of atraumatic, progressive, left index finger distal interphalangeal joint flexion weakness manifesting as difficulty firing his service weapon. He denied any pain, numbness, or paresthesias. MRI revealed flexor digitorum profundus (FDP) and flexor pollicis longus (FPL) atrophy, prompting electrodiagnostic query of anterior interosseous nerve syndrome. EMG demonstrated myotonic discharges (MDs) in the left FPL, pronator quadratus (PQ), abductor pollicis brevis (APB), extensor indicis (EI), and bilateral first dorsal interossei (FDI), fibrillation potentials in the FPL and PQ, and polyphasic motor unit action potentials in the FPL, PQ, APB, EI, and bilateral FDI.

Setting: EMG LabAssessment/

Results: Based on electrodiagnostic results, additional workup was conducted to assess for a myopathic disorder. Anti-cN1A Ab for sIBM was negative. Repeat EMG 3.5 months later demonstrated profuse MDs in all sampled left arm and leg muscles including the deltoid, triceps, FDI, vastus lateralis, gastrocnemius, and tibialis anterior. Genetic testing subsequently revealed two expanded alleles in the DMPK gene, consistent with myotonic dystrophy, type 1 (DM1).

Discussion: Distal myopathies with isolated finger flexor weakness are infrequent, with sporadic inclusion body myositis (sIBM) most well documented. Prominent finger flexor weakness, however, is often observed in myotonic dystrophy, the most common adult-onset muscular dystrophy, preferentially involving the FDP. Though non-specific, EMG can confirm electrical myotonia when clinical myotonia is absent, guiding further work-up.

Conclusion: DM1, a multi-systemic autosomal dominant disorder, is the most common inherited myopathy featuring prominent finger flexor weakness. We present a case of DM1 initially characterized only by left index finger flexion weakness. Given significant clinical variability, finger flexor weakness may be the first manifestation in early or mild disease, and clinicians should consider DM1 in addition to more common musculoskeletal and neuromuscular conditions to ensure timely and accurate diagnosis.​

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/trigger-finger-palsy-in-a-police-officer-as-initial-manifestation-of-myotonic-dystrophy-type-1/