Steroid Myopathy

Most common amongst the drug induced myopathies. The risk of steroid myopathy increases with the dose and duration of use. It typically is a proximal myopathy, preferentially affecting the hip girdle muscles. Relapse of the myositis needs to be distinguished from steroid myopathy. This quandary may occur in patients who initially improved but then started developing progressive muscle weakness following long-term corticosteroids treatment, because it can cause type II muscle fiber atrophy. Features that would suggest a steroid myopathy as opposed to relapse of myositis would be a normal CK, and absence of muscle membrane irritability on EMG. In contrast, patients who become weaker during prednisone taper, have increased serum CK levels, and abnormal spontaneous activity on EMG are more likely experiencing a flare of the myositis. Serum CKs can be elevated in patients with no objective weakness or can be normal or only mildly elevated in patients with active disease.

One should look for red flags in patients who have been on steroids and referred for weakness. Generally, the steroid myopathy patient does not complain of pain but the myositis patient does. It is important to consider avascular necrosis of head of femur (AVN) or distal bone infarcts when a patient complain of hip or groin pain. Order imaging, CT/MRI in these cases.

EDx: Motor and sensory nerve conduction studies are normal. The needle EMG typically is normal unless the myopathy is severe. In this situation, low-amplitude, short-duration MUPs may be seen in the proximal muscles. Of note, abnormal spontaneous activity is not seen. This point is often very useful in differentiating PM from steroid myopathy. It is not uncommon for patients with PM to be treated with steroids, respond well initially, and then note a progression of weakness. In this case, it may be very difficult to differentiate recurrent or undertreated PM from steroid myopathy on clinical grounds. The presence of abundant abnormal spontaneous activity strongly suggests PM, rather than steroid myopathy, as the cause of the weakness.

Chronic fatigue. Patient reports fatigue is her main problem. Reviewing her history, it is clear that her symptoms of fatigue preceded steroid use in 2018. She was started on corticosteroid by her then PCP for presumed multiple sclerosis based on MRI findings of nonspecific hyperintensities and symptoms of fatigue. The pattern in her history is one of feeling better when on prednisone and feeling worse when it is either tapered or discontinued. She also notes when on prednisone, apart from fatigue, her shortness of breath and also achiness/pain in her lower back improves. She has been going back and forth in this pattern, on and off steroids for more than 4 years.

Given her history of fatigue prior to onset of steroid, conditions such as Polymyalgia rheumatica need to be considered given putative history of fibromyalgia. There is nothing in the history to suggest an inflammatory myopathy. Of note, she remains preoccupied by the diagnosis of MS.

On exam, she demonstrates mild weakness of proximal muscles of her lower extremities, however, it is not reliable as she gives reduced effort and demonstrated giveaway weakness. She also demonstrates a similar exam of proximal muscles of her arms and there is limitation in the right arm due to pain, likely from history of rotator cuff tear.

The risk of steroid myopathy increases with the dose and duration of use. It typically is a proximal myopathy, preferentially affecting the hip girdle muscles. She has waddling gait and as per history has proximal muscle weakness in her lower extremities. However, this is confounded by her active musculoskeletal issues, lower back pain, sacroiliac joint dysfunction for which she get ESI injections. She has history of right rotator cuff tear, knee arthroplasty, arthritis of knee/menisceal tear.

The risk of steroid myopathy increases with the dose and duration of use. It typically is a proximal myopathy, preferentially affecting the hip girdle muscles. She has waddling gait and as per history has proximal muscle weakness in her lower extremities. However, this is confounded by her active musculoskeletal issues, lower back pain, sacroiliac joint dysfunction for which she get ESI injections. She has history of right rotator cuff tear, knee arthroplasty, arthritis of knee/meniscal tear.

An inflammatory myopathy is unlikely although this quandary may occur in patients who initially improve in the setting of an established inflammatory myopathy but then start developing progressive muscle weakness following long-term corticosteroids treatment, because it can cause type 2 muscle fiber atrophy. Features that would suggest a steroid myopathy as opposed to relapse of myositis would be a normal CK, and absence of muscle membrane irritability on EMG. Her EMG was reported as an indeterminate study which does not help. Needle examination demonstrates a few motor unit potentials of short duration in bilateral lower limbs. There was no muscle membrane irritability. There is no electrodiagnostic evidence of a large fiber peripheral polyneuropathy or a mononeuropathy of the right or lower extremities. Although the report did not make any comment of ruling out a lumbosacral radiculopathy, needle EMG did not reveal any evidence of active or chronic neurogenic changes in any of the muscles tested. In contrast to the above, in inflammatory myopathies , patients who become weaker during prednisone taper, have increased serum CK levels, and abnormal spontaneous activity (muscle membrane irritability) on EMG. These patient are more likely experiencing a flare of the myositis. Generally, the steroid myopathy patient does not complain of pain but the myositis patient does.

Steroid side effects, sequelae. She has developed sequelae of steroid side effects to include Cushingoid features, skin atrophy, bruising, steroid acne vs acne rosacea (unclear). She has fluid retention and weight gain. She has not had any monitoring since being on steroids DEXA, prophylaxis for pneumocystis, calcium and vitamin D, although she is on PPI.

PLAN:

I would recommend her PCP taper her off prednisone completely and her symptoms monitored after she is off prednisone. It is during that setting a true picture can emerge. She complains of fatigue after being off prednisone for 4 weeks, she may be referred to me for further evaluation. Alternatively, she may need a muscle biopsy to check for steroid induced myopathy.

She may be referred to a rheumatologist for evaluation of polymyalgia rheumatica.

Labs: CK, ESR, CRP, RA, CCP, ANA with reflex to 7 connective tissue disease antibodies, SPEP/SIFE, celiac disease panel, paraneoplastic autoantibody evaluation, and anti-AChR-ab.