Case Index

PATIENT CASE STUDIES
Case 1 2/16 Introduction


Case discussion

This is a 34-year old farmer who presented with a three year’s history of increased difficulty with performing his chores. On retrospect he believed his symptoms may have started 10 years ago. The course had been very slowly progressive over this time. He complained of stiffness in his hands, especially in cold weather. He could drink cold liquids without adverse effects. The patient’s father had suffered with diabetes mellitus and a neurological condition characterized by slowly progressive weakness and stiffness.

On examination he was awake, alert, attentive with fluent speech. There was marked frontal baldness and bilateral cataracts. Visual fields were full to confrontation. Extraocular movements were full without nystagmus. Eye closure and opening was normal. The face was expressionless with hollow temples and cheeks. The masseter and temporalis muscles were moderately atrophic. Tongue and palatal movements and swallowing were normal. Deltoids ware mildly atrophic. Neck flexors were very weak (4/5). Power was mildly reduced in deltoids, wrist extensors and long finger flexors. There was delayed relaxation of grip. Power was normal in the lower extremities. Deep tendon reflexes (DTRs) were normal (2) and symmetric.

  1. Summarize the Case in 1-2 sentences.

    This is a 34 year old male, farmer, with 10 years of progressive stiffness and weakness with a family history of similar condition. On examination he has frontal balding, cataracts, atrophy, weakness and myotonia with normal DTRs.

  2. Discuss lesion localization on the basis of the physical examination.

    Muscle (note myotonia, atrophy with normal dtrs)

  3. Discuss underlying pathogenesis on the basis of clinical course.

    The course is progressive over several years, suggesting a degenerative (biochemical) process.

  4. Indicate one likely clinical diagnosis. List (or classify) alternative diagnoses.

    Myotonic dystrophy Classification of myotonias
    1. sodium channel diseases e.g. hyperkalemic periodic paralysis
    2. Protein kinase-related disease: myotonic dystrophy
    3. Chloride channel diseases e.g. Thomsen’s myotonia congenita

  5. Indicate 2 ancillary tests that would assist in confirming or refuting the clinical diagnosis. Indicate the test results that would confirm the clinical diagnosis.

    EMG would show repetitive decrementing discharges by irritating the muscle membrane Amplification of the protein kinase (myotonin kinase or MT-PK) gene by polymerase chain reaction (PCR) will reveal an abnormally increased number of CTG repeats (more than 50).

  6. Indicate complications of the disease and ancillary tests that would help evaluate them.

    Cardiomyopathy with arrhythmias and heart failure: EKG
    Diabetes mellitus: fasting blood sugar
    Cataracts: slit lamp examination
    Hypogonadism: endocrinological evaluation

  7. Discuss how the underlying pathophysiology is relevant in the management of this patient.

    Abnormality in MT-PK, important in phosphorylating ion channels, leads to lack of phosphorylation of the sodium channel with prolonged channel opening. There is perpetuation of muscle action potential and contraction. Drugs that block sodium channels e.g. phenytoin tend to improve the myotonia.

    Identifying the increased CTG repeats explains anticipation (earlier and more severe presentation in offspring), genetic imprinting (more severe form of congenital myotonic dystrophy in offspring of female patients), helps in confirming